Search

The purpose of this letter is to report a new optoelectronic device which consists of a wirelessly controllable driver circuitry and a slender implantable optical probe. Instead of the conventional silicon substrate, the probe is based on GaN material growing on a sapphire substrate. Thin-film blue micro light-emitting diodes ( $\mu $ LEDs) with a total optical power density of 176.9 mW/mm2 at 1 mA are directly fabricated at the probe by semiconductor device fabrication technologies. In a further research, we integrate a yellow $\mu $ LED on the probe to enable optical stimulation of both excitatory and inhibitory neurons. Besides, we adopt Bluetooth 4.0 wireless communication protocol; therefore, light emitting from the $\mu $ LEDs can be remotely controlled by a terminal with a distance as far as 20 m. The driver is also equipped with an accelerometer, a power management module, and a system-on-chip (SoC), and they are energized by a rechargeable lithium battery that has up to 10-h battery life. The whole device is a little bit bigger than a coin and weighs approximately 6 g. The probe has a length of 1.65 cm and a thickness of $150~\mu \text{m}$ . These features make the device suitable for a broad variety of optogenetic experiments.

A kind of SiGe heterojunction phototransistor with gradual coupled ridge waveguide based on silicon-on-insulator (SOI SiGe GRC HPT) is designed and optimized to improve its optical responsivity and working speed. When the width and length of the ridge waveguide are optimized as 3um and 20um separately, the ridge waveguide based on SOI provide the same limitation for TE mode and TM mode and the suitable propagation path for incident light. The maximum characteristic frequency of SOI SiGe GRC HPT is 102GHz, its saturation current is 20mA and its optical responsivity is 0.5 A/W.

By replacing the common Si substrate with the silicon-on-insulator (SOI) substrate, a low dark current, high responsivity and high response speed novel SiGe heterojunction phototransistor (HPT) detector is illustrated in this paper. The dark current of novel SOI-based SiGe HPT is as low as 0.91nA. The maximum responsivity of novel SOI-based SiGe HPT is 3.86A/W, a 37.86% improvement than the value obtained from common Si-based SiGe HPT. The maximum photo-characteristic frequency (f T , ph ) reach up to 26.43GHz, improved by1.94 times.

In this paper, the working mechanism and high characteristics of an InP/InGaAsP uni-traveling-carrier (UTC) double hetero-junction phototransistor (DHPT) has been analyzed. The UTC-DHPT employs a heavy doping base and two hetero-junctions to realize UTC structure to ease the contract between HPT responsivity and HPT working speed. Optical responsivity and optical transit frequency are analyzed physically through illustrated several kinds of paramistic capacitors in BE junction and BC junction under different electrical bias, optical bias and combined electrical and optical bias in this work. The results show that three-terminal (3T) working mode with combined electrical bias and optical bias in base achieves a highest maxim fT of 120GHz at collector current of 30mA and keeps the same optical responsivity (37.5A/W) compared with two-terminal (2T) working mode.

A second order differential filter with Q-enhancement and tunable active inductor is presented. The design technique for a tunable Q-enhancement SiGe HBT active inductor operating in the wide RF-band for the filter is described. Multi-regulated Cascode circuit is employed to enhance the quality factor Q by increasing the output impedance. Tunable active resistor is introduced to boost the tuning ability of the active inductor. Employing the proposed active inductor, the center frequency of the filter is tuned in the frequency of 1.05~2.45GHz by adjusting the bias current, Q reducing with different bias current can be compensated via tuning the feedback effective resistance of the active inductor, and Q has almost constant value of 209~225 at the frequency of 2.15GHz.

The effects of buried oxide (BOX) layer on the capacitance of SiGe heterojunction photo-transistor (HPT), including the collector–substrate capacitance, the base–collector capacitance, and the base–emitter capacitance, are studied by using a silicon-on-insulator (SOI) substrate as compared with the devices on native Si substrates. By introducing the BOX layer into Si-based SiGe HPT, the maximum photo-characteristic frequency f t,opt of SOI-based SiGe HPT reaches up to 24.51 GHz, which is 1.5 times higher than the value obtained from Si-based SiGe HPT. In addition, the maximum optical cut-off frequency f β,opt, namely its 3-dB bandwidth, reaches up to 1.13 GHz, improved by 1.18 times. However, with the increase of optical power or collector current, this improvement on the frequency characteristic from BOX layer becomes less dominant as confirmed by reducing the 3-dB bandwidth of SOI-based SiGe HPT which approaches to the 3-dB bandwidth of Si-based SiGe HPT at higher injection conditions.

In this paper, the optical gain characteristics and optical high frequency characteristics of an InP-based uni-traveling-carrier double heterojunction phototransistor (UTC-DHPT) are illustrated. The detailed analysis of UTC effects on those perfomaces show that UTC transport mechanism successfully weaks the space charge effect in the collector junction and breaks the limitation of low mobility of the holes. Compared with traditional single heterojunction phototransistor (SHPT), UTC-DHPT improves its processing ability of high power optical signal and provides high saturation current, high responsivity and high response speed simultaneously.

The two-dimensional temperature profile of a power SiGe HBT with traditional uniform emitter finger spacing is calculated, which shows that there is a higher temperature in the central region of the device. With the aid of the theoretical analysis, an optimized structure of the HBT with non-uniform emitter finger spacing is presented. The peak temperature is lowered by 23.82 K, and the thermal resistance is also improved by 15.09% compared with that of the uniform one. The improvements above are ascribed to the increasing the spacing between fingers, and hence suppressing the heat flow from adjacent fingers to the center finger. Based on the analytical results, two types of HBTs with uniform emitter finger spacing and non-uniform emitter finger spacing are fabricated and their temperature profiles and thermal resistance are measured. The measured results agree well with the calculated results, verifying the accuracy of the calculations. For the HBT with non-uniform emitter finger spacing, the peak temperature and the thermal resistance are improved markedly over a wide biasing range compared with that of the uniform one. Therefore, both the calculated results and the experimental results verify that the optimized structure of power HBT with non-uniform emitter finger spacing is superior to the uniform emitter spacing structure for enhancing the thermal stability of power devices over a wide biasing range.

The thermal-electrical characteristics of SiGe HBTs with three kinds of Ge profiles (box, trapezoidal and triangular) in the base are investigated in this paper. The results show that SiGe HBTs with trapezoidal and triangular Ge-profile could improve the peak temperature, non-uniformity of surface temperature distribution, and the sensibility of the gain and cutoff frequency to temperature compared with SiGe HBT with box Ge profile. However, these properties of SiGe HBT with triangular Ge profile are superior to that of trapezoidal Ge profile.

In this paper, an ultra-wideband (3.1∼10.6GHz) active variable attenuator is designed. Π-attenuator circuit topology and SiGe HBTs active devices are employed to achieve high gain dynamic range. LC series negative feedback at emitter is used to achieve flat gain, and RC shunt negative feedback is employed to achieve higher linearity. Furthermore, a matching network is considered for input impedance matching. The active variable attenuator is simulated and verified by using Agilent ADS design kit. The results indicate that the gain dynamic range reaches 40dB, the gain flatness is below 3 dB, the S11 is lower than −10 dB, voltage standing wave ratio (VSWR) is below 1.52dB, and the input third order intercept point (IIP3) is 15dBm when the voltage changes from 0.7 ∼ 1.8V in the frequency band of 3.1 GHz to 10.6 GHz.

Large scale optoelectronic monolithic integration for optical fiber communication makes more and more optoelectronic active devices and passive components integrate into a single chip. It is necessary to provide enough wide gain spectrum to satisfy the requirement from each device. In this paper, based the analysis on the gain spectrum of InGaAsP/InP quantum well, the dependence of its gain spectrum bandwidth on the well width and doping concentration was derived. An asymmetric quantum well with the same doping concentration and different well width was design to realize the destination. The simulation results prove that the asymmetric quantum well indeed make the gain spectrum wider. Then the asymmetric quantum wells were grown successfully by low pressure MOCVD at 665°C. The full width at half maximum (FWHM) of 115nm was observed in its amplified spontaneous emission (ASE) spectrum, which was flatter and wider than that of the symmetric quantum wells.

The noise figure of SiGe HBT for low noise amplification is analyzed and its intrinsic minimum noise figure is expressed analytically. Four types of SiGe HBTs with different transistor geometry of emitter stripe width, emitter stripe length and base stripe number were fabricated using a state-of-art SiGe HBT technology. The considerations involved in the judicious choice of biased current and transistor geometry are explored through theory data and measuring results. A conclusion is drawn that an optimum noise figure can be achieved by proper choice of biased current and transistor geometry with longer emitter length and more base stripe number.

On-chip spiral inductors with high quality factors are very important in many RF circuits. In this paper, spiral inductors are analyzed to study the influence of substrate and spiral structure on an inductor's performance in the multi-GHz frequency range. Firstly, the inductors with different substrate conductivity, thickness and permittivity of the dielectric layer are compared, and a general guide is given that the substrate of a good performance inductor should be light impurity, the dielectric layer should be thick, and use a low k material. And then, this paper presents a novel spiral structure with gradually reduced metal width and space from outside to inside, which can help to alleviate the problems of the magnetic field intensity of a spiral inductor increasing gradually from outside to inside. Compared to conventional inductor, the maximum Q of inductor using gradually changed structure increases by 13.66%, thus the results have corroborated the validity of the proposed method.

A dual wavelength-selectable InGaAsP/InP distributed feedback (DFB) laser with a complex-coupled Bragg grating is presented. An n-doped reverse layer is buried periodically in the index-coupled Bragg grating, which causes a spatial modulation of the carrier concentration in the active region, and so induces the weak gain-coupled to the index-coupled grating. Two wavelengths of 1.51 um and 1.53 um are realized under different work conditions. The side mode suppression ratios (SMSRs) of both wavelengths reach 40 dB benefiting from the single-mode character of the complex-couple grating. This device can be used in coarse wavelength division multiplexer (CWDM) communication system as the light source because of its low-cost and convenience.

The effect of lateral structure parameters of transistors including emitter width, emitter length, and emitter stripe number on the performance parameters of the active inductor (AI), such as the effective inductance Ls, quality factor Q, and self-resonant frequency ω0 is analyzed based on 0.35-μm SiGe BiCMOS process. The simulation results show that for AI operated under fixed current density JC, the HBT lateral structure parameters have significant effect on Ls but little influence on Q and ω0, and the larger Ls can be realized by the narrow, short emitter stripe and few emitter stripes of SiGe HBTs. On the other hand, for AI with fixed HBT size, smaller JC is beneficial for AI to obtain larger Ls, but with a cost of smaller Q and ω0. In addition, under the fixed collector current IC, the larger the size of HBT is, the larger Ls becomes, but the smaller Q and ω0 become. The obtained results provide a reference for selecting geometry of transistors and operational condition in the design of active inductors.

For device analysis and optimization, a model based on Transfer Matrices Method was built to simulation the performance of a new integrated device. This novel DFB laser was composed of two serial sections to provide selectable wavelengths. The periods of two Bragg gratings were different and were chosen to achieve a spacing of 20nm between the two corresponding Bragg wavelengths. The model is more simple and convenient to simulate optical integrated device than other direct simulation methods used before. The simulation results prove that this novel waveguide structure of the serial DFB lasers is feasible. The integrated optical device was fabricated and two wavelengths of 1.51um and 1.53um were realized under different work conditions.

Optoelectronic packaging has become a most important factor that influences the final performance and cost of the module. In this paper, low microwave loss coplanar waveguide(CPW) on high resistivity silicon(HRS) and precise V groove in silicon substrate were successfully fabricated. The microwave attenuation of the CPW made on HRS with the simple process is lower than 2 dB/cm in the frequency range of 0 similar to 26GHz, and V groove has the accuracy in micro level and smooth surface. These two techniques built a good foundation for high frequency packaging and passive coupling of the optoelectronic devices. Based on these two techniques, a simple high resistivity silicon substrate that integrated V groove and CPW for flip-chip packaging of lasers was completed. It set a good example for more complicate optoelectronic packaging.

Width varied quantum wells show a more flat and wide gain spectrum (about 115nm) than that of identical miltiple quantum well. A new fabricating method was demonstrated in this paper to realize two different Bragg grating in an identical chip using traditional holographic exposure. A wavelength selectable DFB laser based on this material grown by MOVPE was presented. Two stable distinct single longitudinal mode of 1510nm and 1530nm with SMSR of 45 dB were realized.

High power AlGaAs/GaAs laser diode array (LDA) cm-bars emitting at around 808 nm have been designed and fabricated for applications in diode bumped solid-state laser technology. Both thermoelectric and water coolers were used for thermal management and compared for their heat dissipation efficiency. At a quasi-continuous working condition of 20% duty cycle and 1 kHz, the peak operating power of the LDA is about 61.8 W with an electro-optical conversion efficiency about 38%. The laser operation temperatures determined from redshifts of the laser-emitting spectrum are compatible with direct measurement from thermocouples. Finally, both static and transient thermal analyses were applied to the LDAs using finite element modeling (FEM) and the results match well with the spectral analysis and thermocouple measurement.

In this paper, a quasi-three-dimension theoretical model for the Vertical-Cavity Surface-Emitting Laser with oxide-confined layers is showed. The distributions of the equal-potential line, injected current density, carrier concentration and the optical field distribution in the cavity are calculated self-consistently by the finite difference method. The influences of the light output window's radius and oxide-confined layers window's radius are studied. At the same time, we study the influence of the N-type DBR on some characteristics of the VCSEL. The results show that there would be a large difference with practical VCSEL ifthe N-type DBR layers were neglected.

Deep Ridge InGaAsP/InP Light Emitting Transistors (LET) with ~1.5 μm light emissions have been fabricated and characterized. In the deep ridge LETs, all the light emissions are from the intrinsic base area, which makes them more suitable for high speed direct modulation. A collector emitter voltage (V CE) dependent output power, which has been predicted numerically, is observed experimentally for the first time and may facilitate the use of LETs in optoelectronic integrations. A novel trend of self-heating related saturation of light power with base current is also observed, which is explained by the three port operation of the device. Further, an abnormal common-emitter current-voltage (I-V) characteristic of the deep ridge LETs is shown and is attributed to the non-radiative recombination centers at the ridge side walls. With the good quality of the quantum wells, laser operation at near room temperature is achieved in the deep ridge LET with 800 μm cavity length. With proper surface passivation techniques and device optimizations, performance of the deep ridge transistor based optoelectronic devices can be further enhanced greatly and ultra low power consumption which is highly desirable can be expected.