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Ultrasonography1 and photoacoustic2,3 (optoacoustic) tomography have recently seen great advances in hardware and algorithms. However, current high-end systems still use a matrix of piezoelectric sensor elements, and new applications require sensors with high sensitivity, broadband detection, small size and scalability to a fine-pitch matrix. This work demonstrates an ultrasound sensor in silicon photonic technology with extreme sensitivity owing to an innovative optomechanical waveguide. This waveguide has a tiny 15 nm air gap between two movable parts, which we fabricated using new CMOS-compatible processing. The 20 μm small sensor has a noise equivalent pressure below 1.3 mPa Hz−1/2 in the measured range of 3–30 MHz, dominated by acoustomechanical noise. This is two orders of magnitude better than for piezoelectric elements of an identical size4. The demonstrated sensor matrix with on-chip photonic multiplexing5–7 offers the prospect of miniaturized catheters that have sensor matrices interrogated using just a few optical fibres, unlike piezoelectric sensors that typically use an electrical connection for each element. An optical ultrasound sensor based on a CMOS-compatible split-rib waveguide is demonstrated, offering high sensitivity, broadband detection (measured 3–30 MHz), small size (20 μm) and scalability to a fine-pitch matrix.

We investigate the impact of field effect transistor (FET) transducer size on its sensitivity to biomolecular surface charge density, as would be encountered in a bulk biomolecule concentration measurement. We characterize electrolytically gated transistor sensors fabricated completely using CMOS FinFET technology and analyse a wide range of channel lengths (3000 nm to 450 nm) and widths (1000 nm to 60 nm). We measure saturated density of biomolecules on the transducer surface in order to eliminate variabilities related to association kinetics or affinity effects of the analyte-receptor biomolecules. We use transistor gate voltage shift to quantify the saturated PNA/DNA hybridization signal. We observe no significant dependence of saturated DNA hybridization signal (29.5 ± 3.7 mV) on transistor dimensions for 15 base pair long DNA with an areal density of about $8.3\times 10^{4}$ DNA/ $\mu \text{m}^{2}$ measured in 1.5 mM buffer. We also confirm these experimental findings by 3D TCAD simulations for transistor widths down to 10 nm, with less than 6% variation in voltage transduction sensitivity versus width. TCAD analysis was also performed for scaling of the FET height from 250 nm down to 5 nm, resulting in a similar small drop in voltage transduction sensitivity (~ 5.5% for a 250 nm wide FET and ~ 14.6% for a 10 nm wide FET). These results show that the FET sensor downscaling does not significantly improve or degrade voltage transduction sensitivity to a charge (or molecule) density.

ispartof: 2022 INTERNATIONAL ELECTRON DEVICES MEETING, IEDM ispartof: International Electron Devices Meeting (IEDM) location:CA, San Francisco date:3 Dec - 7 Dec 2022 status: published

In this study, we analyse and discuss some aspects of the production technology, function, and circulation of the metal pins dated to the Middle and Recent Bronze Age (c. 1700/1650-1150 BC) in the territory comprised between western Emilia, Romagna, Verona lowlands and Lombardy plains. The remarkable number of pins (more than 1600), found in settlements and cemeteries since the 19th century, have been collected in a database, which allowed us to draw the distribution maps of 68 types. Through various experiments we investigated in detail the production process and identified which phases required more advanced knowledge/skills. Thanks to this approach, we were able to distinguish three degrees of complexity in the manufacturing process of pins, and to connect typological variability to technology. We therefore observed that some territorial districts, such as Verona lowlands, are characterized by a more significant presence of complex productions. By examining some of the 68 types, selected among those best documented and with a distribution that does not appear random, we advanced hypothesis on the areas of production and use of certain models, thus linking the aspects of technology to those of custom and mobility at the regional level.

Future applications of ultrasound and photoacoustic imaging require a matrix of small and sensitive ultrasound sensors with read-out through a flexible cable. Silicon photonic ultrasound sensors have good prospects: small and sensitive sensors, wafer-scale fabrication, and matrix read-out via single optical fiber using photonic multiplexing. Here, we discuss different types of silicon photonic ultrasound sensors and their applications. This includes our optomechanical ultrasound sensor with extreme sensitivity that is achieved with an innovative optomechanical silicon photonic waveguide in an acoustical membrane. We discuss limitations of state-of-the-art piezoelectric sensors, how silicon photonic sensors overcome these, and applications in medical imaging.

Future applications of photo-acoustic imaging require a matrix of small (wavelength/2) and sensitive ultrasound sensors with read-out through a flexible cable. Integrated optical sensors have good prospects: small and sensitive sensors, wafer-scale fabrication, and matrix read-out via single optical fiber using on-chip optical multiplexing. We propose a new type of opto-mechanical ultrasound sensor (OMUS) in silicon photonic chip technology. By using an acoustically resonant membrane in combination with an innovative split rib-type photonic waveguide, we achieve extremely high sensitivity. We present our experimental results in the frequency range up to 30 MHz.

We report on the smallest silicon FinFETs functioning as biosensors with 13 nm wide fins and 50 nm gate lengths. These electrolytically gated finFETs exhibit a near-ideal subthreshold swing (~65 mV/dec) and a median voltage referred 1/f noise of only ~470 μV2μm2/Hz (at 1Hz, at threshold). Binding biomolecules to the chemically modified gate dielectric surface changes the threshold voltage VT. DNA-PNA hybridization shows a statistically significant signal across all device geometries (50 nm – 10 µm gate length) with a median VT shift of 36 mV for a hybridized 15 base DNA surface density of ~8×1012 cm-2. We obtain a clear signal of 17 mV for a 20 base DNA surface density of ~8×1011 cm-2, which amounts to tens of molecules for a 13 nm wide and 90 nm long device. This is a major improvement compared to our previously reported 250 nm long FETs which picked up ~800 molecules and a significant step forward towards the realization of single molecule sensing with fully integrated silicon FETs. Finally, based on experiment and simulation, we predict single-molecule detection with SNR > 5 to be possible with sub-70 nm finFETs.

One of the possible applications for MEMS-above CMOS or optical MEMS is for inertial/integrated measurement units (IMUs). These have gained the status of mainstream commodities for consumer electronics in the past years and find use in guidance, navigation, attitude control, smart metering, etc. From the simple 1-axis accelerometer, IMUs have evolved to 3 degrees-of-freedom (DOFs) acceleration sensing and eventually to 6DOFs modules, including angular rate sensors. In particular, the synergy of multi-DOF inertial sensors turned out to be key in improving the navigation capabilities of inertial modules. This trend of adding more functionality to existing units goes on. On-chip magnetometer (for e-compass), barometer, thermometer, electronic nose and clocks, are seen as further enhancements of current IMUs, enabling this way the development of novel smart multi-sensor units.

We review recent progress in neural probes for brain recording, with a focus on the Neuropixels platform. Historically the number of neurons’ recorded simultaneously, follows a Moore’s law like behavior, with numbers doubling every 6.7 years. Using traditional techniques of probe fabrication, continuing to scale up electrode densities is very challenging. We describe a custom CMOS process technology that enables electrode counts well beyond 1000 electrodes; with the aim to characterize large neural populations with single neuron spatial precision and millisecond timing resolution. This required integrating analog and digital circuitry with the electrode array, making it a standalone integrated electrophysiology recording system. Input referred noise and power per channel is 7.5µV and

We report for the first time on a BioFET sensor using FinFETs with 10nm wide fins built in a 300 mm pilot line. Our minimally modified finfet process uses a ‘Replacement Gate’ strategy whereby the Si gate is pulled at the end of the process to form the cavity that holds the electrolyte. We used a pMOS FinFET as our electrolytic gate typically has a high work function of 5.0 eV. Changing the pH or binding biomolecules to the gate dielectric surface changes the threshold voltage (VT). Measuring the VT shift provides high sensitivity due to our high-quality gate dielectric. The median voltage referred 1/f noise of only ~500 μV2μm2/Hz (at 1Hz, at threshold), is significantly lower than other reported bioFETs. We obtain a pH sensitivity near the Nernstian limit of 57 mV/pH for HfO2. Drift of the sensor has been found to be adequate at -1 mV/hour. Finally, we have verified our device to act as a biomolecular transducer. We find the VT shift due to surface bound biomolecules for DNA grafting and PNA-DNA hybridization to be as expected from simulation. Based on our quantification of transduction and simulations we project which single molecule signal-to-noise ratios could ultimately be obtained in the future.

Large-scale neural recording requires more advanced and denser brain interfaces. This paper describes the design and fabrication of the CMOS-based Neuropixels neural probe, which integrates a high-density micro-electrode array and a high channel count to enable large-scale electrophysiology in small animals. Miniaturization and scalability aspects are also discussed here.

This chapter provides an introduction in the simulation and design of integrated photonic microsystems. Using optical beamformers as case study, with applications in LiDAR or wireless optical telecommunication, basic building blocks for photonic integrated circuits (PICs) are introduced. Besides the discussion of their key performance metrics, their modeling and purpose in optical phased array sub-systems, the chapter extends to the simulation of their grouped performance assembled in a simple scanner.

Ultrasonography is widely used in (bio-)medical imaging and especially photo-acoustic imaging is rapidly advancing towards new applications. Future applications require a matrix of small (λ/2) and sensitive ultrasound sensors with read-out through a thin and flexible cable [1]. We target ∼15 MHz ultrasound for e.g. catheter-based intravascular imaging or for freely-moving mouse brain imaging. Integrated optical sensors have good prospects: small and sensitive sensors [2,3], wafer-scale fabrication, and matrix read-out via single optical fiber using on-chip wavelength-division multiplexing (WDM) [4]. Polymer waveguide ring-resonator showed good sensitivity and bandwidth [2] but large device footprint hampers WDM. Silicon photonic waveguides are less susceptible to direct ultrasound but opto-mechanical ultrasound sensors (OMUS), with the photonic resonator integrated in an acoustically resonant membrane, showed high sensitivity [3].

The high index contrast silicon-on-insulator platform is the dominant CMOS compatible platform for photonic integration. The successful use of silicon photonic chips in optical communication applications has now paved the way for new areas where photonic chips can be applied. It is already emerging as a competing technology for sensing and spectroscopic applications. This increasing range of applications for silicon photonics instigates an interest in exploring new materials, as silicon-on-insulator has some drawbacks for these emerging applications, e.g., silicon is not transparent in the visible wavelength range. Silicon nitride is an alternate material platform. It has moderately high index contrast, and like silicon-on-insulator, it uses CMOS processes to manufacture photonic integrated circuits. In this paper, the advantages and challenges associated with these two material platforms are discussed. The case of dispersive spectrometers, which are widely used in various silicon photonic applications, is presented for these two material platforms.

This paper presents a fast design strategy for MEMS capacitive pressure sensors with sealed cavities. Based on circular Kirchhoff-Love plate theory and the perfect gas law, the underlying analytical model allows for a rapid and accurate evaluation of the sensitivity of the sensors, crucial for improving their design in function of the reference pressure applied in the sealed cavities. The accuracy of the new model is demonstrated by comparing its predictions with more computationally expensive simulation techniques (high-order parametric element and three-dimensional finite element models) and with experimental measurements performed on a 300 µm diameter membrane fabricated using the Poly-SiGe platform developed at imec.

A composite, capillary-driven microfluidic system suitable for transmitted light microscopy of cells (e.g., red and white human blood cells) is fabricated and demonstrated. The microfluidic system consists of a microchannels network fabricated in a photo-patternable adhesive polymer on a quartz substrate, which, by means of adhesive bonding, is then connected to a silicon microfluidic die (for processing of the biological sample) and quartz die (to form the imaging chamber). The entire bonding process makes use of a very low temperature budget (200 °C). In this demonstrator, the silicon die consists of microfluidic channels with transition structures to allow conveyance of fluid utilizing capillary forces from the polymer channels to the silicon channels and back to the polymer channels. Compared to existing devices, this fully integrated platform combines on the same substrate silicon microfluidic capabilities with optical system analysis, representing a portable and versatile lab-on-chip device.

This paper reports on the development of a CMOS compatible capacitively actuated optomechanical phase shifter for visible light, demonstrated on a 200mm PECVD SiN photonic platform The phase shifting was demonstrated using Mach-Zehnder interferometers.

Herein, we report about the monolithic integration of a unique photonic stack on top of a CMOS imager using a dedicated fabrication process. The system key components consists of silicon nitride (SiNy) optical waveguides, sloped input mirror, grating in/out-couplers, and copper-based vertical mirrors defining the resonator boundaries. The stack is optimized for operation in the NIR range (800–900nm). Up to the authors' knowledge, this is the first demonstration of a fully integrated photonic stack including a sloped metal mirror combined with SiNy waveguide technology. The photonic build-up can be used for various applications among them is absorption spectroscopy as demonstrated hereafter.

We investigate niobium oxide (NbO) as an alternative waveguide material for applications in the visible spectral range. NbO has a refractive index ranging between 2.3 and 2.35, which is about 25% higher than SiN, the most widely used material for waveguides in the visible spectral range. This increased index contrast between NbO and the cladding material allows to fabricate optical components with much smaller footprint, and consequently to increase the density of photonic integrated circuits substantially. We benchmark this waveguide platform to imec’s CMOS compatible PECVD SiN platform and observe fairly similar loss numbers for both materials.

We present a low-cost integrated nanophotonic lab-on-a-chip platform suitable for point-of-care (POC) biomarker analysis. The sensor chip included in the platform contains multiplexed Mach–Zehnder interferometers with an on-chip optical spectral analyser consisting of an arrayed-waveguide grating. The sensor chip is fabricated in silicon nitride material, which makes it compatible with consumer-electronics-grade sources and detectors, leading to the possibility of low-cost instrumentation. The nanophotonic sensor chip exhibits a detection limit of 6 × 10−6 RIU (Refractive Index Units), which is in the same order of magnitude as the reported values for state-of-the-art evanescent wave sensors. The sensor chip is biofunctionalised with specific bioreceptors and integrated into a polymer microfluidic cartridge. The POC instrumentation platform contains optical excitation and read-out sub-systems and dedicated on-board software for real-time analysis of patient samples. To demonstrate the versatility of the platform, we present results both on the detection of an antigen related to tuberculosis directly in urine samples using a laboratory prototype and on the detection of a protein biomarker (CRP) related to inflammation using the integrated instrument., This work was funded by the European Commission under the FP7 project Pocket (grant 610389). The nanoB2A is a consolidated research group (Grup de Recerca) of the Generalitat de Catalunya and has support from the Departament d'Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya (2014 SGR 624). The ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa programme of the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, Grant no. SEV-2013-0295).

In vivo recording of neural action-potential and local-field-potential signals requires the use of high-resolution penetrating probes. Several international initiatives to better understand the brain are driving technology efforts towards maximizing the number of recording sites while minimizing the neural probe dimensions. We designed and fabricated (0.13- $\mu$ m SOI Al CMOS) a 384-channel configurable neural probe for large-scale in vivo recording of neural signals. Up to 966 selectable active electrodes were integrated along an implantable shank (70 $\mu$ m wide, 10 mm long, 20 $\mu$ m thick), achieving a crosstalk of $-\text{64.4}$ dB. The probe base (5 $\times$ 9 mm $^2$ ) implements dual-band recording and a 171.6 Mbps digital interface. Measurement results show a total input-referred noise of 6.4 $\mu$ V $_{\mathrm{rms}}$ and a total power consumption of 49.1 $\mu$ W/channel.

Poly-SiGe can be used for monolithically integrating Micro/Nano-ElectroMechanical Systems (M/NEMS) with its driving circuitry in a MEMS-last approach. For these applications, it is important to have poly-SiGe films with a low tensile stress, a low resistivity and a high deposition rate. This paper presents a systematic procedure for the simultaneous optimization of these 3 properties for CVD deposited ultrathin (100+/-5nm) poly-SiGe films by using the grey-Taguchi approach. Seven process variables were identified as important parameters for controlling the deposition process and the resulting film properties, namely the deposition temperature, the silane, germane, diborane and hydrogen flow rate, the chamber pressure and the shower head-heater spacing. By using 4 different levels for each process variable, 32 unique experiments were defined based on an L32 orthogonal array. The optimal combination of process parameters was determined by applying the grey relational analysis (GRA) for multiple performance characteristics. The analysis of variance (ANOVA) showed that the deposition temperature has the highest influence on the multi-performance characteristics (contributing ~41%). The projected optimized process resulted in a 100nm-thick poly-SiGe film with a tensile stress of 43MPa, a very low resistivity of 1.39m@?-cm, a deposition rate of 0.34nm/s, a germanium concentration of 87%, a cauliflower surface morphology with a root-mean-square roughness of 4.2nm, an elastic modulus of 101+/-0.81GPa and a strain gradient of -2.0x10^-^2/@mm. The optimized film is expected to be desirable as structural layer for M/NEMS applications such as nanoswitches, nanoresonators, biosensors etc.

Silicon photonics is rapidly emerging as a mature technology platform for the fabrication of photonic integrated circuits. It builds on the technology base of the CMOS-world and allows to implement advanced photonic functions on a small footprint chip with high accuracy and yield. For operation at telecom wavelengths above 1 micrometer one typically uses silicon-on-insulator wafers with waveguides with a silicon core. For short-wavelength operation, below 1 micrometer, one can use a silicon nitride (SiN) core instead of a silicon core. This results in a platform for operation in the visible and near infrared, with moderately high refractive index contrast and low loss photonic components. Operation at short wavelengths can be beneficial for a variety of reasons, including the possibility to use low cost high performance sources and detectors and the compatibility with sensing in an aqeous environment. The SiN CMOS-platform has been used to demonstrate a variety of spectroscopic sensing functions. In essence the SiN chips may contain sensing structures, whereby the evanescent tail of the guided light is interacting with the analyte, as well as spectrometric functions to read out the spectrum resulting from the interaction with the analyte. This approach has allowed to demonstrate refractive index biosensors, spontaneous Raman spectroscopy and surface-enhanced Raman spectroscopy. In the latter case the SiN waveguides are enriched with gold nano-antennas to enhance the local field strength seen by the analyte. The spectrometric functions can be based on arrayed waveguide gratings, echelle grating spectrometers or Fourier Transform spectrometers.

This work demonstrates, for the first time, the use of a post deposition laser annealing technique to realize operational SiGe MEMS devices at deposition temperatures as low as 210 °C. The patterned amorphous SiGe layers are treated by an excimer laser to induce crystallization. After the laser treatment, SiGe devices with good electrical and mechanical properties, such as contact resistivity values to a TiN electrode as low as 4.9 × 10 −7 Ω cm 2 and a strain gradient of −1.6 × 10 −6 μm −1 , are obtained. Devices such as an array of functional capacitive test structures and capacitive switches are realized.

This paper presents an attractive poly-SiGe thin-film packaging and MEM (microelectromechanical) platform technology for the generic integration of various packaged MEM devices above standard CMOS. Hermetic packages with sizes up to 1 mm2 and different sealed-in pressures ( ~ 100 kPa and ~ 2 kPa) are demonstrated. The use of a porous cover on top of the release holes avoids deposition inside the cavity during sealing, but leads to a sealed-in pressure of approximately 100 kPa, i.e. atmospheric pressure. Vacuum ( ~ 2 kPa) sealing has been achieved by direct deposition of a sealing material on the SiGe capping layer. Packaged functional accelerometers sealed at around 100 kPa have an equivalent performance in measuring accelerations of about 1 g compared to a piezoelectric commercial reference device. Vacuum-sealed beam resonators survive a 1000 h 85°C/85%RH highly accelerated storage test and 1000 thermal cycles between -40°C and 150°C.

This paper evaluates the performance characteristics of a new miniaturized lateral capacitive accelerometer with a high bandwidth as well as a high sensitivity, utilizing a low thermal budget SiGe MEMS technology. The accelerometer combines a 4 μm SiGe structural layer thickness with a small capacitive sensing gap of 500 nm, leading to an improvement in sensitivity along with large bandwidth and a reduction in overall dimension compared to conventional accelerometers, which have gaps in the order of 1 μm. The accelerometer studied here is targeted for a maximum operational range of ±2 g.

Poly-SiGe can be used to process Micro Electro-Mechanical Systems (MEMS) directly above standard CMOS. In this work, the use of different surface pre-treatments, such as a CF"4 clean or a Ti/TiN metallic interlayer, to remove unwanted interfacial oxide between a poly-SiGe MEMS structural layer and a poly-SiGe MEMS electrode in the anchor region, is explored. The effect of these treatments on anchor strength and resistivity is studied. Also the effect of the anchor design itself, on the overall anchor characteristics, is investigated. Both the CF"4 pre-deposition treatment and the Ti/TiN interlayer are found to improve the anchor resistance and strength of the SiGe-SiGe anchors. In addition, using a Ti/TiN layer has the benefit of a lower strain gradient non-uniformity compared to using the CF"4 clean.

In this work, the lateral etching of the sacrificial high density plasma (HDP) oxide by anhydrous vapor HF (AVHF) together with ethanol vapor is characterized for SiGe microelectro-mechanical systems (MEMS) structures. An extensive design of experiment (DOE) is carried out to study the impact of the process conditions on etch rate (ER) and within wafer uniformity (UWiW). Two wafer level automated techniques, critical dimension scanning electron microscopy (CD SEM) and high resolution profiler (HRP), are compared to replace the manual inspection method performed at die level. It is found that each 25Torr increment in process pressure doubles the ER in the 75 Torr - 125 Torr range. Each 150sccm increment in AVHF flow rate increases the ER 1.3~1.5 times in the 300 sccm - 600 sccm range. Based on the reproducible ER (~80 nm/min) and the UWiW (~10%) of the process of record (POR) as measured by CD SEM, a statistical process control (SPC) is set up for this process condition.

In imec's 200mm fab a dedicated poly-SiGe above-IC MEMS (Micro Electro-Mechanical Systems) platform has been set up to integrate MEMS and its readout and driving electronics on one chip. In the Flemish project Gemini the possibilities of this platform have been further explored together with the project partners. Three different demonstrators were realized: mirrors for display applications, grating light valves (GLV) and accelerometers. Whereas the mirrors and GLVs are made with a ~300 nm thick SiGe structural layer plus optical coating, the SiGe structural layer thickness for the accelerometers is 4µm in order to improve the capacitive readout of in-plane devices. The processing and measurement results of these functional demonstrators are shown in this paper. These new demonstrators reconfirm the generic nature of the SiGe MEMS platform.

We have demonstrated a MEMS memory device utilizing an array of cantilevered AFM probe tips fabricated directly on standard CMOS, and integrated with a ferroelectric media on a movable platform by wafer bonding. The MEMS process uses low-temperature poly-SiGe to fabricate cantilevers with sub-100nm tips and suspended metallization to connect the tips to read-write circuitry in the CMOS. The probe tip array interfaces with a single-crystal PZT media film upon which data densities on the order of Tb/in^2 have been demonstrated. The mover is actuated electromagnetically with>100 micron stroke and sub-nm position sensing. The cantilever, mover and cap wafers are integrated using AuSn solder-based wafer bonding.

Poly-crystalline Silicon-Germanium is a promising structural material for post-processing Micro Electro-Mechanical Systems (MEMS) above CMOS due to its excellent mechanical and electrical properties when deposited at CMOS compatible temperatures. In this work an optimized process to deposit high quality crystalline poly-SiGe layers with low stress, low strain gradient and good within-wafer uniformity at a manufacturable throughput is developed. The process used to deposit the layers is based on a combination of CVD and PECVD SiGe depositions. Firstly, the CVD SiGe process has been extensively characterized to the extent that the influence of thickness, Ge concentration and B concentration on film stress and strain gradient is now well understood. Then the interaction between the PECVD SiGe and the underlying CVD layer has been investigated. This combined knowledge enables specific tailoring of the CVD-PECVD SiGe stack to give the desired strain gradient for a certain layer thickness.

Hybrid integration of living cells and electronic circuits on a chip requires a high-density matrix of sensors and actuators. This matrix must be processable on top of CMOS devices and must be bio-compatible in order to support living cells. Recent studies have shown that the use of nail structures combined with a phagocytosis-like event of the cell can be exploited to improve the electrical coupling between a cell and a sensor. In this paper, two CMOS-compatible fabrication methods for sub-micron nails will be presented. The biocompatibility and proof-of-concept is demonstrated by the culturing of PC12 neuroblastoma cells. Electrical functionality is shown by simultaneous stimulation and recording of pig cardiomyocyte cells. Biocompatibility aspects for more demanding cortical cell cultures have been addressed in a preliminary assessment.

We report on miniaturized optical spectrometers integrated on a photonic integrated circuit (PIC) platform based on silicon nitride waveguides and fabricated in a CMOS-compatible approach. As compared to a silicon on -insulator PIC-platform, the usage of silicon nitride allows for operation in the visible and near infrared. Furthermore, the moderately high refractive index contrast in silicon -nitride photonic wire waveguides provides a valuable compromise between compactness, optical loss and sensitivity to phase error. Three generic types of on -chip spectrometers are discussed: the arrayed waveguide grating (AWG) spectrometer, the echelle grating or planar concave grating (PCG) spectrometer and the stationary Fourier transform spectrometer (FTS) spectrometer. Both the design as well as experimental results are presented and discussed. For the FTS spectrometer a specific design is described in detail leading to an ultra -small (0.1 mm2) footprint device with a resolution of 1 nm and a spectral range of 100nm. Examples are given of the usage of these spectrometers in refractive index biosensing, absorption spectroscopy and Raman spectroscopy.

Silicon photonics typically builds on a silicon-on-insulator based high-index-contrast waveguide system. Silicon nitride provides an alternative moderate-index-contrast system that is manufacturable in the same CMOS environment. This paper discusses the relative benefits of both platforms.