Search

This paper presents a pair of trapezoid microcantilever probes with a monolithic micromachined thermocouple for inspecting the electrical and thermal properties of Micro-LED. To meet testing requirements, one of the microcantilevers was designed as a single-layer Ni structure for electrical conduction, while the other one, which consists of n-type poly-Si, SiO₂ and Ni layers, was used for temperature sensing. Both microcantilevers were fabricated by using Si bulk micromachining, thin film deposition, and electroplating processes. Fabrication result shows the length of each probe is about 78 μm and 118 μm, and the thicknesses of the microcantilevers and probe tip are 7.2 μm and 5.5 μm. Experiment results depict that the thermocouple junction between Ni layer and poly-Si achieves a good ohmic contact, and the measured sheet resistances for poly-Si and electroplated Ni are 150 Ω /sq and 0.01 Ω /sq. This suggests that the induced thermoelectric voltage can be generated and detected in response to a temperature difference. Mechanical tests verified that the probes provide an available elastic deflection to guarantee that the probe tips can exactly contact the Micro-LED electrodes, with a low contact force. The thermoelectric characteristics of the device have been further confirmed and calibrated on the basis of the measurement results of a commercial mm-sized LED in cooperation with an infrared camera. For the subject of the Micro-LED chip with a square size of 75 μm, its electrical and thermal properties were successfully determined, as the measured chip temperature is 52 °C at the applied current of 100 μA. [2021-0053]

This study presents the design and implementation of a MEMS capacitive tactile force sensor with polydimethylsiloxane (PDMS) filler for in-process and in-use modulation of the sensing range and sensitivity performance. The presented MEMS tactile force sensor consists of a loading unit with driving electrodes, PDMS filler, and a sensing unit. By varying input voltages on the driving electrodes (either in curing process or in-use), the stiffness of the PDMS filler as well as the loading unit can be modulated. Thus, the sensitivity and sensing range of the presented tactile force sensor was modulated accordingly. Since each sensor has its own driving electrodes and electrical routings, different input voltages can be applied to modulate the PDMS for each individual sensor. As a result, tactile sensors of different sensitivities and sensing ranges can be simultaneously fabricated and monolithically integrated on the same chip using the presented approach. The tactile sensors were implemented using TSMC $0.18~\mu \text{m}$ 1P6M standard CMOS process together with the in-house post-CMOS releasing and the polymer filling processes. Experiments demonstrate the capabilities of implementing various tactile sensors with different sensing ranges and sensitivities on a single chip by the in-process and in-use modulation techniques. Through the in-process and in-use modulation, the presented CMOS-MEMS tactile sensors show the sensing window: (1) for sensitivity modulation: 8.6 fF/N to 219.1 fF/N, and (2) for sensing range modulation: 30 mN to 270 mN.

This article proposed a novel design for the monolithic micro-LED array, directly integrated with a sapphire microreflector. Its resolution was 300 dpi. Theoretically, each micro-LED pixel owns an individual sapphire microreflector which can directly concentrate rays from an emitting source. Therefore, this study proposed that the optical crosstalk between neighboring micro-LED pixels could be suppressed and the contrast of the micro-LED array improved; as this would be especially beneficial for display. The simulation results showed that the increased thickness of the sapphire microreflector could further improve the optical performance of the micro-LED array. For the fabrication process, the key technology was an integrated process involving the inductively coupled plasma (ICP) etching technology for sapphire and micro-LED fabrication, which was used to fulfill the proposed and reference micro-LED arrays. The measurement results showed that the sapphire microreflector could effectively concentrate the emitting rays and increase the contrast of the micro-LED array. In addition, it also indicated that the inclination angle of the microreflector could further improve optical performance. Therefore, this approach was verified to be capable of improving the performance of the micro-LED display.

This study demonstrates the integration of thermoelectric type MEMS infrared (IR) sensor with plasmonic metamaterial absorber (PMA) through a standard CMOS process platform to improve the responsivity of MEMS IR sensor in a specific range of wavelength. Based on an existing thermoelectric IR sensor with the serpentine film structure, the proposed device further combines with a Metal-Insulator-Metal (MIM) type PMA. The absorber consists of a top antenna layer, a middle dielectric spacer, and a bottom reflector, and the metal and dielectric films in the standard CMOS process are exploited in this study to implement the MIM design. The advantage of narrow linewidth in CMOS process can meet the need of critical dimensions for MIM antennas. The absorption wavelength can be adjusted by varying the pattern and dimension of antennas. The MIM PMAs are designed in the coupling regime, and hence the shifting of absorbed wavelength caused by the variation of antenna dimensions from fabrication can be prevented. The feasibility of the presented MIM PMA is demonstrated by simulations and experiments. The absorption spectra measured by FTIR show the capability of proposed MIM PMAs in extending the absorption range of far-infrared. Measurement results also indicate that under the same sensor footprint and the equal number of thermocouples, the device integrated with the proposed MIM PMA has a 20 percent improvement in responsivity as well as detectivity.

This study presents a backside loading design inductive tactile sensor with the monolithic integration of thermometer. Based on the commercially available standard complementary metal-oxide-semiconductor (CMOS) process (the TSMC $0.35\mu \text{m}$ 2P4M CMOS process) and the in-house post CMOS processes, the sensing chip is designed and implemented. The electrical connection is further achieved by using the flip-chip bonding process, and hence the breakage of bonding wires by the tactile load can be avoided. The CMOS sensing chip consists of the magnetic sensing coil and the polysilicon RTD (resistive thermal detector). Moreover, a cavity is defined on the backside (silicon substrate) of CMOS chip to act as a mold for the polymer filler as well as the housing for the chrome steel ball contact interface. The tactile force will cause the polymer deformation and chrome steel ball displacement, and further lead to the magnetic flux change on the sensing coil. Thus, the tactile force is detected by the inductance variation of magnetic sensing coil on the CMOS chip. Moreover, the temperature variation is detected by the resistance change of RTD thermometer, and the in-situ temperature monitoring during tactile loading is achieved. The force response of the proposed tactile sensor and the temperature response of the thermometer have been characterized. The influence of temperature variation on the tactile sensor has also been calibrated. Moreover, the characteristics of the thermometer on sensing chip at different contact conditions are also investigated.

This letter presents a simple approach to implement the inductive-type micro tri-axial tactile sensor by integrating a complementary metal–oxide–semiconductor (CMOS) chip with sensing coils and a stainless steel sheet (as the sensing interface) using polymer encapsulation. In addition to the component integration, the polymer layer is exploited as the spring for the tactile sensor. The proposed CMOS-MEMS inductive tri-axial tactile sensor presents several features and advantages as follows: 1) the gap-closing inductive sensing approach is used for normal force ( ${Z}$ -axis) detection; 2) the area-change inductive sensing method is adopted for shear forces’ ( ${X}$ -axis and ${Y}$ -axis) detection; 3) the compact sensing coil array is implemented using the standard CMOS process; and 4) the polymer is employed as the encapsulation layer to cover and integrate the rigid stainless steel sheet sensing interface and the CMOS chip, while also acting as the spring to avoid the fragile suspended thin-film structure. To demonstrate the concept, a CMOS sensing chip with a $2\times 2$ coil array is fabricated using the Taiwan Semiconductor Manufacturing Company standard process and is further integrated with a stainless steel sheet prepared by laser machining. The measurements indicate that the typical fabricated tri-axial inductive tactile sensor exhibits a normal load sensitivity ( ${Z}$ -axis) of 2.9 nH/N, an ${X}$ -axis shear force sensitivity of 17.4 nH/N, and a ${Y}$ -axis shear force sensitivity of 15.3 nH/N.

This study presents a piezoelectric MEMS tweeter with novel structure and electrodes designs (Fig. 1) for two-way excitation to enlarge its bandwidth, which can meet the requirement of in-ear applications. The proposed design has two merits: (1) Dual-ring spring design: to offer two resonant modes with piston vibrations to contribute sound pressure, (2) Distribution and excitation of driving electrodes design: to achieve the two-way excitation to drive the two required vibration modes. Thus, this proposed design could enlarge the bandwidth at the high frequency range with decent sound pressure level (SPL). Measurements in the standard ear simulator with 2Vpp input voltage demonstrate the presented tweeter has a significant bandwidth improvement of 14 kHz∼30 kHz (for the ±10dB range of SPL (72 dB SPL∼92 dB SPL)).

This study demonstrates the capacitive type humidity sensor design with novel fringe-effect sensing electrodes and polyimide-pillar array, as shown in Fig. 1. The sensor is implemented by the TSMC 0.18µm 1P6M CMOS platform and also monolithically integrated with thermometer and micro heater for performance enhancement. The presented humidity sensing unit has two major merits: (1) polyimide-pillar array: to enhance water vapor absorption and improve the response time; (2) fringe capacitive sensing electrodes: for easy integration with the polyimide-pillars and also to prevent the cross-talk from heater; and the proposed design also features with: (3) vertical integration of micro heater: to prevent water vapor condensation; (4) backside silicon etching: for thermal isolation; (5) monolithic integration of thermometer: for signal calibration. Measurements show the response time of proposed humidity sensor have 43% enhance after plasma etching, and also demonstrate the performances of heater and thermometer. Simulations further indicate a 1.5-fold sensing signal enhancement compared with parallel electrodes.

This study proposes a novel design to implement a triaxial tactile force sensor, as shown in Fig. 1. The tactile force sensor is fabricated by TSMC standard CMOS process. The normal and shear forces sensing capabilities are achieved by three independent sensing components monolithically integrated on a single chip. Capacitive sensing membrane forms the normal force detection element and piezo-resistive bridges form the shear force detection elements. Merits of the design include (Fig. 2): (1) fully-clamped square-diaphragm array as the capacitive-type normal force sensing element: flexible only in out-of-plane direction (z-axis) to detect the normal load and avoid the cross-talk from shear forces; (2) clamped-clamped beam with Wheatstone bridge circuits as the piezo-resistive shear force sensing elements: flexible only in one in-plane direction (x-axis or y-axis) to detect the single axis share load, and the cross-talk from normal load is removed by the Wheatstone bridge circuits. Measurement results show the sensitivities of the proposed tri-axial tactile force sensor are 1.26 fF/N in z-axis, 2.043 mV/N in x-axis, 2.248 mV/N in y-axis and have less than 10% overall crosstalk.

Objective. Recording and stimulating neuronal activity across different brain regions requires interfacing at multiple sites using dedicated tools while tissue reactions at the recording sites often prevent their successful long-term application. This implies the technological challenge of developing complex probe geometries while keeping the overall footprint minimal, and of selecting materials compatible with neural tissue. While the potential of soft materials in reducing tissue response is uncontested, the implantation of these materials is often limited to reliably target neuronal structures across large brain volumes. Approach. We report on the development of a new multi-electrode array exploiting the advantages of soft and stiff materials by combining 7-µm-thin polyimide wings carrying platinum electrodes with a silicon backbone enabling a safe probe implantation. The probe fabrication applies microsystems technologies in combination with a temporal wafer fixation method for rear side processing, i.e. grinding and deep reactive ion etching, of slender probe shanks and electrode wings. The wing-type neural probes are chronically implanted into the entorhinal-hippocampal formation in the mouse for in vivo recordings of freely behaving animals. Main results. Probes comprising the novel wing-type electrodes have been realized and characterized in view of their electrical performance and insertion capability. Chronic electrophysiological in vivo recordings of the entorhinal-hippocampal network in the mouse of up to 104 days demonstrated a stable yield of channels containing identifiable multi-unit and single-unit activity outperforming probes with electrodes residing on a Si backbone. Significance. The innovative fabrication process using a process compatible, temporary wafer bonding allowed to realize new Michigan-style probe arrays. The wing-type probe design enables a precise probe insertion into brain tissue and long-term stable recordings of unit activity due to the application of a stable backbone and 7-µm-thin probe wings provoking locally a minimal tissue response and protruding from the glial scare of the backbone.

This study presents the design of thermocouples to enhance the detectivity of thermoelectric (TE) infrared (IR) sensor. The IR sensor is implemented using the standard TSMC CMOS processes. Merits of the design include: (1) to enlarge the width of thermocouple to minimize the influence of thermal noise, (2) no need to change the existing structure design. The proposed design is shown in Fig. 1. The IR sensor with higher detectivity (which means its easier for signal processing) is a design target. Measurement results demonstrate the proposed IR sensor can achieve 21.7% detectivity improvement and sustain the responsivity within 8.4% decrease in total. It indicates that this simple approach can successfully enhance the total performance of TE IR sensor.

We have monolithically integrated a PZT thin film and "buried" Si piezoresistive sensors for piezoelectric MEMS actuators. The PZT thin film works as a sensor as well as an actuator, but the static position sensing is difficult unlike piezoresistors. On the other hand, the process compatibility of PZT with a Si piezoresistor is unclear, because the Si piezoresistor is very sensitive to impurities, surface charges and contaminations. In this study, PZT MEMS cantilevers with the "buried" Si piezoresistive sensors were successfully fabricated by a proposed fabrication process, and the material composition was analyzed by secondary ion mass spectrometry (SIMS) to study the process compatibility. The fabricated devices were actuated by the PZT thin film, showing the first resonance frequency at 6.3 kHz. The integrated position sensor could successfully detect the amplitude with a sensitivity, non-linearity and noise floor of 0.037 mV/pm, 0.75% and 1 × 10-6 V/√Hz, respectively.

This study presents a broadband piezoelectric MEMS microspeaker based on the design of cantilever array and novel driving method in Fig. 1a. Two main points are featured in this study: (1) The design of multi-way microspeaker with cantilever array: to improve the bandwidth of the microspeaker. The SPL is enlarged in selected frequency ranges contributed by the different resonant frequencies of each cantilever; (2) The out-of-phase driving of each cantilever after resonance: to prevent the sound pressure cancellation between cantilevers resulted from the 180° structural phase shift after resonance. In comparison, Fig. 1b shows two different driving approaches. Measurement results show the highest SPL of 110dB at 1540Hz in ear simulator system with a driving voltage of 2V pp under 4mm2 diaphragm area. In addition, out-of-phase driving promises an improvement of 27dB at 3.7kHz where sound pressure cancellation took place. A broadband frequency response is obtained between 100Hz~10kHzwith an SPL of 70dB or higher with out-of-phase driving. With multi-way cantilever array design and in-phase/out-of-phase hybrid-driving, a high SPL and broadband microspeaker is realized.

This study realizes MEMS IR sensors using novel hybrid silicon etching processes on the CMOS platform. The processes include DRIE and XeF2 silicon etching, which can control the undercut depth and release the MEMS structure respectively. Such silicon etching processes exhibit three merits: (1) the undercut depth can be increased to enhance the responsivity of MEMS IR sensors in the atmosphere, (2) the process is conducted at the front side of the chip and the inherent CMOS dielectric layers act as the hard mask to avoid the alignment issues from the traditional approach using backside etching, and (3) this process is CMOS-compatible and benefits the construction of CMOS-MEMS IR sensors. The simulation and measurement results successfully demonstrate the enhancement of the responsivity of MEMS IR sensor through the hybrid silicon etching processes.

In this paper, a thin film PZT MEMS actuator feedback controlled with integrated buried piezoresistors is reported. Two PID controllers were used to implement a phase-locked loop (PLL) with automatic gain control (AGC). The amplitude of the device could be precisely controlled by using the buried piezoresistors. The proposed fabrication process was compatible with both components. The positioning accuracy and drift as small as 5 ppm and 95 ppb/min, respectively, could be obtained by the proposed system. In addition, the bias stability and the white noise were reduced by 90%. The results presented here show significant improvement of the precision and stability of the PZT-based device.

This paper proposes a new design of a Micro-LED display with a sapphire micro-reflector array. This novel technology uses an ICP etching process to fabricate a V-shaped trench in sapphire substrate. With the microloading effect, a specific sapphire micro-reflector is created under each Micro-LED, which can be used to converge the light rays and therefore, improve the display quality of a Micro-LED. In this study, the feasibility of a sapphire and GaN etching process and the optical performance of a Micro-LED have been evaluated and measured by experimentation. It was confirmed that the proposed Micro-LED display has an improved lighting performance, while increasing 55% in maximum brightness.

This study presents the piezoelectric MEMS microspeaker design in Fig. 1a with four triangular plates, a connection mass, and dual driving electrodes (inner and outer electrodes) to increase the sound pressure level (SPL). By integrating the microspeaker on chip, for example the array with 5 microspeakers in Fig. 1b, the SPL could be further increased. This study exhibits two merits: (1) The inner and outer electrodes on triangular plates (Fig. 1c) are driven with 180° out-of-phase to actuate the piston mode of structure to increase the SPL; (2) The connection mass synchronizes the vibration of the four plates to reduce the gap size surrounding the plates for low frequency sound pressure enhancement. Measurements show the SPL enhancement of the proposed dual electrode driving is 9.5dB as compared with the single (inner or outer) electrode driving. Measurements in the standard ear simulator indicate the presented microspeaker array has the SPL of 81.4dB at 100Hz and the SPL of 84.7dB at 1kHz. The results show that the presented design exhibits good SPL at low frequency. Moreover, the proposed microspeaker array (5 microspeakers) presents ±3dB bandwidth between 100Hz∼2.1kHz, and the highest SPL of 118.1dB at 11.9kHz with only 2V pp driving voltage.

This study monolithically integrates a metal-insulator-metal-based (MIM) plasmonic metamaterial absorber (PMA) with a thermoelectric (TE) infrared (IR) sensor using standard TSMC CMOS platform. The proposed design extends the strip-via releasing hole structure in [1] to further integrate MIM absorber with TE IR sensor. Such design exhibits three merits: (1) the line width requirement of MIM absorber is achieved by CMOS process, (2) the absorption peaks of MIM absorbers can be modulated by pattern designs in the epsilon-near-pole region, and (3) the MIM absorbers can be designed to broaden the absorption spectrum of IR sensor. In application, the absorption spectrum of IR sensor is designed within $8-14\mu \mathrm{m}$ in this study for human detection application. Measurement result demonstrates the integration of MIM absorber and IR sensor can achieve 21% responsivity improvement and the measured absorption spectrum matches with simulation.

This study presents a monolithic integration of pressure, humidity and temperature sensing units to achieve an environmental sensing hub (Fig. 1). The proposed environmental sensing hub is realized using the TSMC $0.18\mu \mathrm{m}$ 1P6M CMOS platform, and follow-up in-house post-CMOS processes. The presented environmental sensing hub has three merits: (1) single-side microfabrication processes: for monolithic integration of pressure, humidity, and temperature sensors, (2) vertical integration design: for the temperature sensor and the high sensitive pressure sensor with corrugated diaphragm, and (3) novel capacitive humidity sensor design: pillar sensing electrodes array and surrounded polyimide filler for response time enhancement. Measurements show performances of proposed environmental sensing hub are: sensitivity of pressure sensor with corrugated structure is 0.969fF/kPa (0.197fF/kPa for reference type w/o corrugated structure), humidity sensor with sensitivity of 2.897fF/%RH and response time of 12.1 seconds, and resistance temperature detector with sensitivity of 0.26%/°C.

This study presents a novel approach and the electrode design to drive two particular vibration modes of the structure to improve the frequency range of the piezoelectric MEMS microspeaker. Extending the advantage of the spring-diaphragm structure to enhance low-frequency sound pressure level (SPL) in the previous work [1], the proposed design in this study not only sustains low-frequency SPL by the piston mode of the diaphragm actuating by the edge electrodes, but also further increases high-frequency SPL to improve frequency range by the drum mode excited by the central electrode on the diaphragm. Measurements in the standard ear simulator depict that the proposed design has a significant SPL enhancement after the first resonant peak and meanwhile maintains the performance at low frequencies. From 2.6 kHz ∼ 20 kHz, the proposed design shows an improvement of more than 15 dB SPL over the reference design.

This research reports a monolithically integrated Humidity/Thermometer/Pressure sensor to realize an environment sensing hub. The environment sensing hub is designed and implemented using the TSMC $0.18 \mu \mathrm{m}$ 1P6M CMOS platform and the follow-up double-side post-CMOS micromachining processes. Features of this study are: (1) Small footprint with less packaging effort: monolithic integration of H/T/P sensors on a single chip, (2) Fast response time of relative-humidity (RH) sensor: removal of backside silicon by double-side post-CMOS process to enhance vapor diffusion of capacitive RH sensor. (3) Double-side post-CMOS process: simultaneously fabricating backside cavities for H/P sensors. Measurement results indicate the performances of the environment sensing hub: humidity sensor with sensitivity of 4.06fF/%RH and response time of 3.1sec (15.7sec for the reference type of conventional design), and pressure sensor with sensitivity of 0.79fF/kPa, thermometer with response of 15.8mV/°C.

This study demonstrates a novel vertically integrated double-bridge design for tri-axial piezo-resistive force sensor using commercial available CMOS process (Fig. 1). The normal and shear force sensing capabilities are achieved by measuring the signal changes of three independent Wheatstone bridges embedded in two bridges (fixed-fixed beams). The proposed sensor design has three merits: (1) two orthogonal bridges enable the directional sensing for shear forces, (2) piezo-resistors and electrical routings embedded in two bridges are designed to form three independent Wheatstone bridges for tri-axial force sensing, (3) the footprint reduction of the sensing chip is achieved by the vertical integration of two bridges. The measurements demonstrate the feasibility of tri-axial force sensing, and indicate that the sensitivities of the proposed tri-axial force sensor are, respectively, normal force (Z-axis) −0.18 mV/N, shear force (X-axis) −7.46 mV/N, and shear force (Y-axis) 7.26 mV/N.

This study presents a packaged MEMS acoustic or air pressure sensing module (Fig. 1) to detect the skull vibration for bone conduction microphone (BCM) application. The proposed microphone design has two merits: (1) the packaged module (Fig. 1) enable the skull vibration detection using the MEMS sensor; (2) no sound port is required to remove the environmental and wind noise and to avoid the damage from dust and water (Fig. 1a). The device with the dimensions of $3.5\times 2.65\times 1.48\ \text{mm}^{3}$ is implemented using the packaging and assembly of existing MEMS sensor with polymer diaphragm and metal proof-mass. Measurements show the device has a sensitivity of −39.1dB/g, $\text{THD} at 1kHz, and ±5dB bandwidth for 100Hz∼6.7kHz. Frequency responses of different samples show good repeatability.

This study designs and realizes an improved piezoelectric MEMS microphone with four triangular-cantilevers (Fig. 1) on a commercial 8-inch wafer. As compared with the reference design [1], this study exhibits two merits: (1) special boundary and structure design of the triangular-cantilever for sensitivity enhancement (Fig. 1a); (2) two-stage etching to successively define PZT/electrode and device-Si layers to enable the fabrication of small gaps between triangular-cantilevers for low frequency acoustic sensing enhancement (Fig. 1b). Moreover, the bottom of MEMS microphone chip is bonded (surface mount) on LGA (land-grid-array) for better acoustic performance (Fig. 1c). Preliminary FEM evaluations show the enhancement of proposed type as compare with a reference type (Fig. 2). Measurements indicate the packaged microphone of $1080\ \mu\mathrm{m}$ cavity size: acoustic sensitivity is - 37.54dBV/Pa at 1kHz; ±3dB bandwidth ranges 150Hz to 9.5kHz; noise floor of 20Hz∼20kHz bandwidth and A-weighting is −86.4dBV(A); SNR is 48.9dB(A); measured capacitance of sensing electrode is 410pF at 1kHz; dielectric constant is 250; and loss tangent of PZT is 0.015.

This study realizes an improved signal-to-noise ratio (SNR) MEMS microphone based on piezoelectric sensing principle. In Fig. 1a, the proposed square-shaped and the reference 45-degree right triangle cantilever diaphragm (PZT/Silicon unimorph) arrays are designed and implemented for comparison. The proposed microphone has two merits, (1) enhance SNR by increasing sensitivity: with the same diaphragm area, the proposed square cantilever diaphragm design can provide larger stress and wider stress distribution than the reference type, as in Fig. 1b, which increase the sensitivity. Measurement shows the proposed microphone has a higher SNR of 70.1dB (at 1 kHz). As compared with the reference type, the proposed design has a 2.3dB SNR improvement (at 1 kHz). (2) prevent sensitivity loss at low frequency by reducing the gap between cantilever diaphragms: the proposed arrangement of cantilever diaphragms reduces the gap between the bent cantilever diaphragms (caused by residual stress, as in Fig. 1a) to prevent the low-frequency acoustic loss. Acoustic frequency response measurement shows successful prevention of sensitivity loss at low frequency.

This study demonstrates a novel tri-axial piezo-resistive tactile sensor vertically integrated with a inductive proximity sensor using standard CMOS process (Fig. 1). Normal and shear loads sensing capabilities are achieved by measuring the signal changes of four piezo-resistive cross beams. The proposed sensor design has three merits: (1) the tri-axial tactile sensing unit and the proximity sensing unit can be vertically integrated on one chip, (2) normal and shear loads can be detected by four discrete piezo-resistive sensing elements, (3) the footprint of the chip can be reduced due to the vertical integration of sensing elements. The measurements demonstrate the capabilities of tactile sensing for both normal and shear loads and proximity sensing. The testing results indicate that the proposed tri-axial piezo-resistive tactile sensor shows the normal load (Z-axis) sensitivity of 0.55 mV/N, the X-axis shear load sensitivity of 1.3 mV/N, and the Y-axis shear load sensitivity of 0.76 mV/N.

This study presents a CMOS-MEMS tactile sensor fill-in with dielectric PDMS nanocomposite to batch fabricate and modulate the sensing range and sensitivity (Fig. 1). Merits of the sensor are: (1) Inprocess batch selective modulation by input voltage: apply different voltages on uncured dielectric PDMS nanocomposite fill-in simultaneously, tactile sensors with different sensing ranges and sensitivities are batch fabricated after polymer curing (Fig. 2); (2) In-use selective modulation by input voltage: the sensing range and sensitivity of each tactile sensor can still be modulated after the process by applying voltage on cured dielectric PDMS nanocomposite (Fig. 3). Moreover, sensing range and sensitivity can be further modulated using different dielectric PDMS nanocomposites. The tactile sensor is implemented using TSMC 0.18μm 1P6M CMOS process, in-house post-CMOS releasing and dielectric PDMS nanocomposite filling processes. Measurement results demonstrate the in-process modulation could modulate sensing range (60mN to 100mN) and sensitivity (maximum 2-fold enhancement) Moreover, the in-use modulation could further modulate sensitivity from 1.1fF/mN to 4.8fF/mN and sensing range from 100mN to 35mN.

This study demonstrates a vertically integrated environment sensor with a fluorescence quenching based gas sensor [1] and a resistive temperature detector (RTD) using the TSMC standard CMOS process (Fig. 1a). Features of this study are (Fig. 1): (1) integration of photo-sensors, thermal-isolation structure, temperature, and optical based gas-sensing films using CMOS and polymer dispensing technologies, (2) multiple optical sensors equipped with thermal compensation unit (thermometer) are monolithically integrated, (3) heterogeneous integration with LED can reduce the size of gas sensor, (4) various sensing films can be prepared for multiple gases detection. Measurements show the results of sensitivity at room temperature and under influence of temperature variation. A sensitivity of 19.7 (μA/%) for O 2 (sensing range: 16-50% oxygen concentration) is achieved at room temperature and the sensitivity of the gas sensor decreases from 9.2μA/% to 1.7μA/% as the environment temperature increases from ~40°C to ~80°C. The monolithically integrated thermometer enables the on-site temperature monitoring for sensing signal compensation.

This study presents a novel inductive tactile sensor array with rigid stainless-steel bump sensing interface for 3D micro joystick button application (Fig. 1a-b). The presented micro joystick button design using inductive sensor array and stainless-steel bump interface has several merits: (1) batch process to define and etch bumps on stainless-steel sheet, (2) compact sensing coil array using CMOS platform can distinguish the magnitude and distribution of tactile loads, and (3) polymer as spring and encapsulation layer to cover the rigid tactile bump and CMOS chip without any fragile suspended thin film structure. The design is implemented using standard TSMC 0.35 μm 2P4M CMOS process and in-house post-CMOS processes. Measurements show sensing signals from the proposed sensor array could distinguish the loading conditions for 3D micro joystick button application.

This study designs and implements a metal-oxide semiconductors (MOS) type gas sensor in Fig. 1. The chip is implemented using TSMC 0.35μm 2P4M standard CMOS process and the sensing material is prepared by hydrothermal synthesis method. The gas concentration is detected based on the resistance change measured by the proposed sensor. Features of this study are (Fig. 1): (1) reduction of size through vertical integration of heater and ZnO-SnO 2 gas-sensing films on the CMOS-MEMS structure, (2) reduction of power consumption of the gas sensor through the heater design. In applications, the gas sensor will be used for O 2 concentration measurement. Measurement results show that the sensitivity of O 2 concentration sensing is improved from 0.093%/% to 0.3%/% (within O 2 concentration of 16-50%), and the power consumption is reduced from 477mw to 32mw by varying the heater design.

Extending the approach in the previous work [1], this study presents a piezoelectric actuation MEMS microspeaker with novel spring design to achieve high sound pressure level (SPL) at low frequencies for in-ear applications. The soft PZT/Si unimorph springs enable larger out-of-plane displacement to enhance SPL. With the proposed spiral-spring design, longer spring length (compared with [1]) and lower resonant frequency are achieved to improve SPL at low frequencies. Moreover, the spiral spring has simple stress distribution during actuation to ease electrical routings and also increase the net driving output for piezoelectric films, thus the dual driving electrodes to increases diaphragm out-of-plane displacement and SPL is achieved. Measurements demonstrate 79.5dB SPL (72.6dB SPL for [1]) with only 2V pp driving voltage and 1mm2 diaphragm area at 1kHz in a 3cm long canal. Furthermore, 106.8dB SPL is observed with 15V pp at 1.85kHz without any structure damage.

This study presents a novel molding/encapsulation/integration approach to realize tactile-bump and sensing-interface for the inductive tactile sensor (Figs.1a-b). Two sensing-interfaces are available using wafer-level silicon molding for proposed tactile sensor: (1) chrome steel ball encapsulated in polymer tactile bump (Fig. 1a), (2) MPC (Magnetic Polymer Composite) embedded in polymer tactile bump (Fig. 1b). Figs.1c-d show the design and sensing scheme of the proposed inductive tactile sensor. The proposed molding/encapsulation/integration approach offers three merits for the inductive tactile sensor: (1) chrome steel ball self-assembled/fixed in Si cavity for polymer molding, (2) tactile-bump and MPC sensing-interface integrated in Si cavity by polymer molding, and (3) polymers of different properties (e.g.: stiffness, magnetic property) integrated using multi-steps molding processes. The inductive tactile sensor of three different designs is successfully demonstrated.

This study presents novel capacitive tactile sensor designs with vertically integrated double deformable electrodes array (Fig. 1) based on the standard CMOS platform. The proposed designs have also been implemented by the TSMC 0.18 μm 1P6M standard CMOS process and in-house post-CMOS fabrication. The merits of the presented tactile sensors are as follows, (1) vertically integrating double deformable structures with embedded sensing electrodes (Fig. 1c) by using the multi-stacked thin films of CMOS process; (2) electrically connecting the deformable and fixed electrodes to enhance the initial capacitance C 0 and the capacitance change ΔC under the same footprint; (3) discretizing the sensor into a 5×5 sensing unit array to dramatically reduce the warpage of deformable structures introduced by residual stresses; (4) enhancing sensitivity of tactile sensor using the design of deformable structures. Measurement results show a sensitivity of 0.8%/N for the double-membrane design, and 1.4%/N for the membrane-spring design.

This study presents a MEMS IR-laser beam scanning system consisted of the micro Fresnel lens and linear comb actuators. The merits of this study is to fabricate and further integrate the binary phase Fresnel lens, micro springs, and micro electrostatic actuators through the silicon micromachining processes to achieve the proposed IR-laser beam scanning system. Thus, the difficulty and problem resulted from assembly can be prevented. The proposed IR-laser beam scanner is a spring-mass system driven by linear comb-drive actuators, and operates at the resonant frequency to enlarge the scanning angle. Measurements indicate the scanner has a resonant frequency of ~2 kHz (exceeds the millisecond minimum response time requirement for application), and a displacement of greater than ±20μm at a driving voltage of V DC =12.5V, V pp =18V. Moreover, the 1550 nm infrared laser beam has a deflection angle of ±6.84°.

This study presents a magnetostrictive type inductive sensing pressure sensor which consisted of a planar coil, CoFeB magnetic films, and a Si diaphragm. As the Si diaphragm deformed by a pressure load, the inverse-magnetostriction effect would cause permeability changes of the CoFeB magnetic films. Thus, the permeability changes as well as the pressure load can be detected by the inductance change of a planar inductor. To demonstrate the feasibility of the proposed pressure sensor, the planar inductor designs of different coil turns and in-plane patterns of magnetic films are fabricated and tested. Preliminary measurements show that the pressure sensors with 6 and 12 coil turns have sensitivities of 0.079 %/kPa and 0.064 %/kPa, respectively. In addition, based on the in-plane pattern design of the magnetic films, the gauge factor could be tuned from 55 to 852.

This study presents the design, fabrication, and testing of a novel capacitive type CMOS-MEMS tactile sensor with vertically integrated sensing structures for enhancing sensitivity, and discretized sensing array design for inhibiting residual stress warpage. The proposed type tactile sensor utilizes polymer buffer above the sensor and polymer fill-in between the vertically integrated sensing structures as force transmission layers. This enables effective force loading onto the sensor, and more importantly, simultaneous deformation of the two vertically integrated sensing structures during force loading, thereby guaranteeing an increase in sensitivity. The enhancement in sensitivity of the proposed tactile sensor was demonstrated to be achieved under the same footprint area. To mitigate warpage issues that may occur due to thin film residual stresses, the sensor was discretized into arrays of separate sensing units. Sensing units are electrically connected in a parallel fashion to ensure maximum capacitance signal. As compared to a reference tactile sensor with conventional sensing electrodes, the proposed design showed a near 1.3-fold enhancement in sensitivity. Measurements also indicate the 5 × 5 array design could tolerate the influence of residual stress. Additionally, effect of operating temperature on initial capacitance (temperature coefficient of offset, TCO) and capacitance change signal during force loadings (temperature coefficient of sensitivity, TCS) were investigated for both the reference and proposed type tactile sensors.

This study presents a bone conduction microphone (BCM) to detect the variation of air pressure resulted from the skull vibration. The presented BCM consists of a commercial MEMS microphone, the sensing circuits, the bulk metal, the deformable polymer diaphragm, and two printed circuit board (PCB) covers. In this design, two chambers and a vibrating spring-mass structure are hermetic sealed by two PCB covers. As the spring-mass structure vibrates, the pressure of one chamber will increase and that of another will decrease. Thus, the vibration could introduce a higher pressure load as well as a larger sensing signal for the BCM. In application, the device with the dimensions of 3.5 × 2.65 × 1.48 mm3 is implemented. Measurements show the device has a sensitivity of −38.8 dBV, THD < 0.48% at 1 kHz with 1 g excitation, and ±5 dB bandwidth for 100 Hz∼6.7 kHz. Frequency responses of different samples show good repeatability. Furthermore, air leakage effect and crosstalk of the skull vibration sensing module have also been investigated in this paper. The results demonstrate the feasibility of the presented BCM.

We developed a lead zirconate titanate (PZT) thin film actuator integrated with buried piezoresistors for the dynamic and static deformation sensing of a PZT MEMS actuator. We demonstrated the fabrication of sol-gel deposited PZT thin film devices combined with buried piezoresistors and proved, for the first time, the process compatibility of these materials. Dopant concentration measured by secondary ion mass spectrometry (SIMS) analysis confirms that the piezoresistor was successfully buried into the device. Motion detection of the fabricated MEMS cantilever actuated by the PZT thin film was successful and consistent with optical measurement as well as design values. From these results, we can conclude that our PZT actuator and piezoresistive sensors can be monolithically integrated. The fabrication process developed here can be used for high-stability piezoelectric MEMS actuators with feed-back control of position.

This study designs and implements the differential MEMS microphone (Fig. 1) to improve its signal-to-noise ratio (SNR) and sensing range using MOSBE process [1]. The microphone has three major merits: (1) achieve Differential MEMS Microphone using top/bottom diaphragm and top/bottom back-plate formed by two poly-Si layers (Fig. 1b); (2) reduce Low Frequency Acoustic Loss by removing release holes and adding surrounding mesa for diaphragm (Fig. 1b); (3) improve Sensing Area and Sensitivity through parallel plate gap-closing capacitance sensing enabled by rigid diaphragm with flexible U-shaped springs (Fig. 1c); and one minor merits: single sacrificial layer to define differential sensing gaps to reduce process induced thickness variation. Measurements indicate microphone of $800\ \mu\mathrm{m}$ “diameter” diaphragm: acoustic differential sensitivity is −40.5dB (Ref: 1V/1Pa) at 1kHz; ±3dB bandwidth ranges 50-20kHz; and the SNR is over 57.8dB.

This study based on piezoelectric actuating principle to design and realize a high sound pressure level (SPL) MEMS microspeaker for in-ear applications. The proposed suspension-spring design enables larger out-of-plane displacement to improve SPL and the piston movement of diaphragm to generate sound waves with better quality. Moreover, applying dual electrode pattern on the suspension springs further enhances diaphragm out-of-plane displacement and SPL. Measurements demonstrate the highest SPL above 100dB at 3.13kHz in a 3cm long canal. SPL higher than 70dB is obtained from 400Hz to 8.5kHz with only 2V pp driving voltage and 1.67mm2 diaphragm. Furthermore, total harmonic distortion (THD) is less than 3% in most of the audio range.

This study demonstrates the monolithic/vertical integration of piezo-resistive tactile and inductive proximity sensing units using standard TSMC CMOS process (Fig. 1). Before contact, the proximity sensing of object is achieved by inductance change of spiral coil; after contact, the tactile load from object is detected by resistance change of bent piezo-resistors (Fig. 1b). The proposed sensor design to offer the proximity/tactile sensing capabilities has four merits: (1) tactile and proximity sensing units can be vertically implemented and integrated on one chip, (2) no interference between two sensing mechanisms to enable sensing units working independently, (3) simultaneous detection for proximity/tactile is achieved to enable continuous object monitoring before/after contact, (4) footprint reduction of sensing chip due to vertical-integrated design. Measurements indicate the sensitivity of tactile unit is 0.73mV/N (loading range: 0-2N), sensing distance of proximity unit is 2.5mm for stainless steel object, and simultaneous/continuous detection for tactile and proximity are also demonstrated.

This study presents a flip-chip integrated CMOS chip with polymer-filler and metal-ball in backside Si cavity for inductive tactile sensor (Figs. 1a-b). By using the polymer-filler and chrome-steel ball as force/sensing interface, the proposed inductive tactile sensor has several merits: (1) cavity on backside Si-substrate for polymer molding and chrome-steel ball housing, (2) dual-stage polymer molding to define polymer-spring and to fix the chrome-steel ball, (3) flip-chip bonding to replace the wire bonding for the electrical connection, and (4) sensing-chip backside loading design for flip-chip bonding. The presented design is implemented using the standard TSMC $0.35\mu\mathrm{m}$ 2P4M CMOS process and in-house post-CMOS processes. Measurements indicate the sensitivity of tactile sensor is 3.2nH/N within loading range of 0-2N, and the monolithically integrated thermometer with TCR of 0.1%/°C is also demonstrated.

This study presents the design, fabrication, testing of the capacitive type MEMS microphone with differential sensing electrodes to improve the sensitivity and signal-to-noise ratio (SNR). Based on an existing trench-refilled MOSBE process platform with two poly silicon structure layers, one Si3N4 electrical isolation layer, and two sacrificial SiO2 layers, the microphone is designed and implemented. The microphone consists of top and bottom diaphragms and backplates. The top diaphragm and bottom backplate form a sensing electrode pair, and the bottom diaphragm and top backplate form the second sensing electrode pair. Moreover, the Si3N4 layer is exploited to partition the structures into three different electrical regions. Thus, the differential sensing MEMS microphone is achieved by using only two polysilicon structure layers. Various auxiliary components such as the central post and the U-shape springs are also developed to realize the differential microphone. Measurements show that the typical fabricated microphone with a footprint of 800μm diameter has the single-ended sensitivities of −45.8dB and -47.2dB (ref: 1V/1Pa), and the SNR is over 52dB. Moreover, the ±3dB bandwidth of the microphone ranges from 50Hz to 22kHz. In summary, the presented microphone has the differential sensitivity of -40.5dB (ref: 1V/1Pa) and the SNR of over 57.8dB.

This paper presents a design concept that uses the impedance effect of a spiral dual-coil array to identify fingerprint patterns. Unlike commercial optical, resistive, and capacitive sensing technologies, this unique dual-coil design enables the measurement of a fingerprint using the effect of the ridges and valleys on electrical impedance. In this study, a typical sensing chip with a 3 × 128 dual-coil array was fabricated by a simple microfabrication process. Variations of the coupling capacitance and mutual inductance were then used to verify the properties of different mediums. For a typical case in ambient air, the measured resonant frequency was 8 MHz, which resulted in a maximum induced current of 1.0 mA and a phase shift of 45.5°. The measurement results for saline solutions with different concentrations showed that mediums with higher conductivity caused larger phase shifts. The sample data resulting from the dual-coil array were successfully used to reconstruct a fingerprint image, with a good match in minutiae.

This study implements the metal-oxide-semiconductor (MOS) type gas sensor using the TSMC 0.35 μm 2P4M process. The gas concentration is detected based on the resistance change measured by the proposed sensor. This design has three merits: (1) low-cost post-CMOS process using metal/oxide wet etching, (2) composite sensing material based on ZnO-SnO2 coating on the CMOS-MEMS structure, (3) vertical integration of heater and ZnO-SnO2 gas-sensing films using CMOS-MEMS and drop casting technologies. Proposed design significantly increase the sensitivity at the high operating temperature. In summary, the sensitivity of presented sensor increased from 0.04%/% (O2/N2) at near room operating temperature to 0.2%/%(O2/N2) at near 140 °C for the range of 5–50% oxygen concentration.

This study presents the approach to implement an electromagnetic type active wireless CMOS-MEMS tactile sensor. The tactile force applied on sensor will deform the flexible polymer and further cause the displacement of rigid chrome-steel ball. Thus, the magnetic flux and the voltage of sensing coil induced by the driving coil are changed, which are employed to measure the tactile load. The proposed tactile sensor has four merits: (1) flexible polymer filler as spring, (2) rigid chrome-steel ball as movable sensing interface (for loading and introducing magnetic flux change), (3) CMOS chip as sensing unit, and (4) sensitivity is enhanced by increasing the driving voltage. Note: no suspended thin film structures are required. The presented design is implemented by the standard TSM C O.18μm CMOS process. Measurements indicate the sensitivity of tactile sensor (with 5Vpp driving voltage) is O.53mV/N with loading range of 0-2.4N.

A complementary metal–oxide–semiconduc-tor (CMOS)–microelectromechanical system (MEMS) accelero-meter with stacked pure oxide layers as mechanical structures was developed. Metal layers were confined to the sensing electrodes and electrical routings; the metal–oxide composite in the CMOS–MEMS accelerometer was distributed in limited regions. This design has two major advantages: 1) the thermal deformation of suspended MEMS structures resulting from a mismatch in the coefficients of thermal expansion of the metal and the oxide in the metal–oxide films is suppressed; and 2) the parasitic capacitance of the sensing electrode routing underneath the proof mass is reduced. Thus, the accelerometer has higher sensitivity and reduced thermal drift. The curvature of the mechanical structures are improved in the temperature span and the noise floor is lowered. In the full temperature span (30 °C–90 °C), change in the radius of curvature per unit change in the temperature was 0.08%/°C for the in-plane accelerometer and 0.37%/°C for the out-of-plane accelerometer. Compared with the typical metal–oxide design, the proposed pure oxide design yielded a >20-fold improvement in radius of curvature change per unit temperature change for the in-plane accelerometer and a fivefold improvement for the out-of-plane accelerometer. Moreover, the noise floor was reduced to 0.40 ( $x$ -axis), 0.21 ( $y$ -axis), and 0.94 mG Hz $^{-1/2}$ ( $z$ -axis), respectively, a 2.2–7.6-fold improvement compared with the metal–oxide design. [2015-0012]