Chee Yee Kwok

A novel multi-input floating-gate MOS four-quadrant analog multiplier

A novel four-quadrant analog multiplier using multi-input floating-gate MOS (MFMOS) transistors has been designed and fabricated using a 2-/spl mu/m double-poly double-metal P-well CMOS process. It is essentially based on the quarter-square technique which relies on the square-law characteristic of the MOS transistor in the saturation region. The multiplier is realized with only four MFMOS transistors and a current source. The input range is 100% of the supply voltage and accepts either differential, single-ended, or floating input signals. Measured nonlinearity and total harmonic distortion are 0.2% and 0.5%, respectively, under full scale input conditions. Input noise is 170 /spl mu/V (rms), giving a 95 dB input dynamic range. The power dissipation is 1.1 mW and bandwidth is 12 MHz. Second-order effects on the multiplier performance have also been analyzed.

Design criteria for bi-stable behavior in a buckled multi-layered MEMS bridge

In this paper, the bi-stability of a buckled multi-layered micro-bridge with elastically constrained boundary conditions is studied theoretically and experimentally. The residual moment due to non-symmetric distribution of residual stress in the layers of the micro-bridge is taken into consideration. The buckled shape model, which characterizes the initial buckled deflection, is employed in this study. A systematic method of designing bi-stable buckled micro-bridges has been developed and applied to multi-layered structures. The method is tested against ANSYS simulation and shown to be in excellent agreement. Two multi-layer micro-bridges have been fabricated: (i) 2.5 µm thick low stress SiO2/1 µm thick high compressive stress SiO2/2 µm thick SCS Si; (ii) 1 µm thick high compressive stress SiO2/2 µm thick SCS Si. The fabricated bridges are tested for bi-stability by thermal actuation and the results agree well with the analysis. The intrinsic bi-stable nature of a buckled micro-bridge can only be guaranteed as long as the residual moment is within a certain threshold value.

Numerical simulation of micro-fabricated zero mass-flux jet actuators

Abstract Computational fluid dynamics can play an important role in the design of microelectromechanical systems (MEMS)-based actuators, allowing an investigation of the underlying physical behavior of devices before proceeding to expensive manufacturing processes. Here, we present the results of a series of numerical simulations of synthetic jet actuators, so-called because they synthesize jets from the working fluid. The primary characteristic of these actuators is that over a cycle, the net mass flux is zero, yet the mean momentum flux is non-zero. The simulations consider both the internal and external flow-fields of a micro-scaled device, with the membrane motion specified using a simplified structural analysis. Key features of the flow in the external, orifice and cavity regions are presented and discussed. The actuator output is observed to vary linearly with a non-dimensional input parameter, and this may guide the design of flow control systems that use synthetic jet actuators. Finally, our fabrication strategy for a MEMS-based synthetic jet actuator is presented.

Integrable active microvalve with surface micromachined curled-up actuator

An integrable electrostatic microvalve consisting of a curled-up cantilever movable part and a square valve orifice comprising of three pyramidal channels in tandem is presented. The curled-up cantilever, which consists of a silicon dioxide beam with a very thin layer of Cr, is formed by surface micromachining. The valve orifice is fabricated by bulk micromachining in such a way as to merge with the surface micromachining process. This process provided better control of the orifice dimensions. Measured switching voltage of 30 volts has been obtained. Linear flow versus differential pressure characteristics have been obtained from this type of triple tandem pyramidal orifice.

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.

Fabrication and characterization of sputtered NiTi shape memory thin films

Sputtering conditions to produce nearly equiatomic NiTi films were studied. Two heat treatment methods, substrate heating (550 ?C) and post-sputter heat treatments (solution heat treatment at 700 ?C and precipitation heat treatment at 400 ?C), were used to crystallize NiTi films. The NiTi films were analysed for their atomic composition, crystal structure, transformation temperatures, residual stress and Youngs modulus. NiTi films produced by rf magnetron sputtering were slightly titanium rich. With appropriate post-sputter heat treatment, NiTi films with phase transformation temperatures within the human body temperature range (34?42 ?C) were produced. The films also demonstrated two-way shape memory training capability.

Theoretical analysis of integrated collimating waveguide lens

An integrated collimating waveguide lens is analyzed for applications which require the focusing of an optical beam onto the waveguide of a planar lightwave circuit. The lens has a refractive index profile which is parabolically graded as a function of height to focus light in the vertical plane, and has a convex front face to focus light in the horizontal plane. Analysis based on the propagation of a Gaussian field is used to design a lens pair which minimizes the optical loss for a given propagation length. The beam propagation method is used to identify fabrication tolerances which may have impact on the performance of the lens pair. The lens pair has application in micro-optoelectromechanical (MOEM) switches based on planar optical waveguide circuits.

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/.