Ruey-Shing Huang

A novel optical accelerometer

A novel accelerometer based on a PIN photo-detector and a micro-machined cantilever-beam-supported optical shutter with seismic mass has been designed, fabricated, and tested. Anisotropic wet etching of <110> orientation silicon in KOH is used to fabricate an optical shutter consisting of evenly spaced vertically etched slots. The shutter, which also constitutes the seismic mass of the accelerometer, is suspended by two cantilever beams. The special structure of the device and the high aspect ratio of the cantilever beams (7.5) permit freedom of the movement for the proof mass (the shutter) on the /spl plusmn/X axis only. The actual size of the device is 3/spl times/4 mm and its amplified output varies linearly from -3.6 V to +3.6 V for accelerations from -84 g to +84 g. The measured resonant frequency of the device is 3.2 KHz. A dual diode structure is chosen for the photo-detector to compensate for temperature drift and the amplified output voltage changes by less than 40 mV for a temperature variation from 25/spl deg/C to 50/spl deg/C.<<ETX>>

A linear electromagnetic accelerometer

Abstract A linear electromagnetic accelerometer has been designed and fabricated from Si 〈100〉 wafers using silicon micromachining techniques. The amplified output voltage of the fabricated device for accelerations ranging from 0 to 50g is measured and the results are in good agreement with computer simulations. The actual size of the device is 4.2 mm × 4.2 mm, its amplified output voltage varies linearly from 0 to 9 V at a rate of 0.175 V/g and the power consumption is less than 2.5 mW, The device structure consists of two planar coils of 12 turns each and a seismic mass supported by two cantilever beams. The principle of operation is based on the variation of mutual inductance between the coils, caused by acceleration forces. This dual-beam structured accelerometer responds linearly to the acceleration force normal to the plane of the mass and the supporting beams; lateral accelerations have almost no effect on the output voltage. Due to the simple structure, batch processing with on-chip signal-conditioning circuitry is possible. The electronic circuitry required is much simpler compared to that for capacitive accelerometers.

A wide-range linear optical accelerometer

Abstract An optical accelerometer has been designed and fabricated using conventional KOH etching of 〈100〉-orientation silicon. The seismic mass acts as an optical shutter and consists of evenly spaced vertically etched slots. The shutter is suspended by two cantilever beams and controls the amount of light flux from a red light-emitting diode (LED) source reaching a PIN diode detector. The special structure of the device and the high aspect ratio (7.5) of the cantilever beams permit freedom of movement for the seismic mass (the shutter) along only one axis. The actual size of the device is 3 mm × 4 mm and its amplified output varies linearly from −3.6 to +3.6 V for static accelerations from −84 g to +84 g . The dynamic response of the device shows a flat relative sensitivity up to 700 Hz and increases to 21.9 dB at 3.2 kHz, which is the resonance frequency. The second harmonic appears at 6.8 kHz with a relative sensitivity of 9.9 dB. A dual diode structure is chosen for the photodetector to compensate for temperature drift and the amplified output voltage changes by less than 40 mV for a temperature variation from 25 to 50 °C when the applied acceleration is zero.

A study on field-emission array pressure sensors

Abstract In view of the specific advantages of using vacuum as the device medium and a field-emission cathode as electron source, a renewed interest in vacuum microelectronics utilizing advanced IC technology is emerging. This paper presents an application of field-emission arrays in a novel pressure sensor. Both cone-shaped and wedge-shaped emitter arrays are studied. Various wet and dry etching techniques for forming the emitter arrays are compared. A combined wet/dry fabrication process is developed to achieve array uniformity and reproducibility. The characteristics of a pressure sensor with an ideal field-emission array are simulated, and methods to take into consideration the non-uniformity of array tips, an inevitable result of the fabrication process, are also discussed. The performance of a fabricated pressure sensor with a cone-shaped emitter array is evaluated.

Simulation and design of field emitter array

Some simulation results about potential, field strength, and emitting current density of cone-shaped emitter arrays are presented. Several important design features about the field emitter array are discussed. The most striking feature is that if one wants to obtain more current from the field emitter array in a given device area, there is a limit to the density of the emitter array due to the emitter tip field strength lowering effect, which is a result of the interaction from nearby surrounding tips. If one reduces the tip radius to increase the field strength a higher current density is compensated by a reduced effective emitting area; therefore, to obtain the highest emitter current for a certain set of designed emitter array geometric parameters a corresponding optimal tip radius needs to be determined.<<ETX>>

An integrated thermo-capacitive type MOS flow sensor

A prototype of a new thermo-capacitive integrated flow sensor consisting of a floating-gate MOS transistor has been developed. Tantalum pentoxide is the dielectric material between the top (control) gate and the floating-gate. The temperature dependence of the dielectric constant is about 375 ppm//spl deg/C. The process flow is compatible with standard MOS process and augmented to include a capacitor module and bulk micromachining. The output voltage change at the flow velocity of 20 m/s is about 26 mV at 57 mW of heater power. The sensitivity in the 0-4 m/s flow velocity region is 4.25 mV(m/s)/sup -1/.

A novel electromagnetic accelerometer

A novel micro-accelerometer based on electromagnetic field induction has been fabricated from Si <100> wafers using silicon micro machining techniques. For this design, measurements of acceleration ranging from 0-50 g have been experimentally demonstrated. The physical structure and a brief description of the fabrication process is given. The actual size of the device is 4.2/spl times/4.2 mm, its amplified output voltage varies linearly from 0-9 V with the rate of 0.175 V/g and the power consumption is less than 2.5 mW. Due to the simple structure a batch processing with on chip signal conditioning circuitry is possible. The required electronic circuitry compared to the capacitive accelerometers is much simpler.<<ETX>>

A silicon thermocapacitive flow sensor with frequency modulated output

Abstract A silicon thermocapacitive gas-flow sensor with frequency modulated output where the shift in the oscillation frequency is related to the gas-flow velocity has been developed. The sensing module, which is fabricated using a MOS-compatible process combined with EDP groove etching, is a capacitor. The dielectric material of the capacitor is r.f.-sputtered SrTiO 3 , the large dielectric constant of which is also temperature dependent. Together with an external 555 IC, the oscillator frequency at zero flow velocity and 250 mW of heater power is 8.7 kHz. The sensitivity is 118 Hz (ms −1 ) −1 in the linear region, wuth 250 mW of heater power.

An analytical model for back-gate effects on ultrathin-film SOI MOSFET's

An analytical model including the semiconducting substrate effect for silicon-on-insulator (SOI) MOSFET threshold and subthreshold operation is presented. The potential drop across the substrate tends to reduce the front-gate threshold voltage as well as subthreshold swing. However, if the substrate or the back-gate surface is accumulated, the substrate effects can be neglected. Five comprehensive operation regions under various bias conditions are distinguished and discussed for the first time.<<ETX>>

A silicon-diode-based infrared thermal detector array

Abstract A new silicon-diode-based infrared thermal detector array (1 × 4) has been developed. The silicon diode, as a temperature-sensing device, is built on a thin cantilever structure that is formed by micromachining. The thickness of the cantilever is about 5 μm. A thin layer of bismuth is evaporated on the cantilever as an infrared radiation absorber. With a cantilever measuring 264 μm × 112 pm × 5 gm and an active area measuring 102 μm × 102 μm, the fabricated detector array yields a responsivity of 5.3 V/W, a detectivity of 2.7 × 10 7 cm Hz 1/2 /W, and a noise equivalent temperature difference (NETD) of 1.7 °C.