N. H. Tea

Micromachined Convective Accelerometers in Standard Integrated Circuits Technology

This letter describes an implementation of micromachined accelerometers in standard complimentary metal–oxide–semiconductor technology. The devices operate based on heat convection and consist of microheaters and thermocouple or thermistor temperature sensors separated by a gap which measure temperature difference between two sides of the microheater caused by the effect of acceleration on free gas convection. The devices show a small linearity error of <0.5% under tilt conditions (±90°), and <2% under acceleration to 7g(g≡9.81 m/s2). Sensitivity of the devices is a nearly linear function of heater power. For operating power of ∼ 100 mW, a sensitivity of 115 μV/g was measured for thermopile configuration and 25 μV/g for thermistor configurations. Both types of devices are operable up to frequencies of several hundred Hz.

Thermoelectric power sensor for microwave applications by commercial CMOS fabrication

This work describes an implementation of a thermoelectric microwave power sensor fabricated through commercial CMOS process with additional maskless etching. The sensor combines micromachined coplanar waveguide and contact pads, a microwave termination which dissipates heat proportionally to input microwave power, and many aluminum-polysilicon thermocouples. The device was designed and fabricated in standard CMOS technology, including the appropriate superimposed dielectric openings for post-fabrication micromachining. By removing the bulk silicon located beneath the device through micromachining, thermal and electromagnetic losses are minimized. The sensor measures signal true RMS power in the frequency range up to 20 GHz with input power in the -30 dBm to +10 dBm range. Over this 40 dB dynamic range, output voltage versus input power is linear within less than /spl plusmn/0.16%. Automatic network analyzer data show an acceptable input return loss of less than -30 dB over the entire frequency range.

In situ conductivity characterization of oxide thin film growth phenomena on microhotplates

Through the use of silicon micromachining, we have developed a microhotplate structure capable of reaching temperatures in excess of 500 °C, onto which thin films have been selectively grown via metalorganic chemical vapor deposition. The microhotplate structure contains surface electrical contacts which permit conductance measurements to be made on films during and after deposition, and therefore presents some unique opportunities for the in situ characterization of growing films as well as for novel gas sensing approaches. We have investigated the deposition of conducting oxides such as SnO2 and ZnO on these microhotplate platforms for gas sensing applications. The conductance of the deposited films has been measured in situ as a function of time, and used in combination with postdeposition thickness measurements to provide insights into the growth rate of the oxide films. Results indicate that our conductance measurements are sensitive, in certain cases, to changes in the film thickness on the order of...

Design and fabrication of micromachined passive microwave filtering elements in CMOS technology

This paper describes a novel implementation of micromachined microwave resonators and filters, coupled with low-loss transmission lines, fabricated in standard CMOS technology. Selective etching of the Si substrate beneath the microwave elements results in significantly lowered transmission loss, improved quality factor and operating frequency range. This allows operation at gigahertz frequencies. Resonators with Q-factors of 20 and resonant frequencies of 2 GHz and 21 GHz are reported which are significant results for standard CMOS technology. A low-pass filter is also reported with a 2.5 GHz cutoff frequency. The resonant and cutoff frequencies are in general adjustable within the 1 to 40 GHz band. These devices are useful for integration with microwave power sensors, and have application in wireless communication systems where low-loss operation above 1 GHz is essential.