High-precision miniature accelerometers based on electron tunneling transducers have been successfully fabricated using bulk-silicon micromachining process. This process has been modified to reduce bi-metal effects and results in greatly-suppressed 1/f noise. A comprehensive system model and a robust controller based on mixed /spl mu/ synthesis have also been developed to close the feedback loop, extend the bandwidth, and withstand accelerometer variations due to micromachining process variations. This accelerometer is a prototype intended for underwater acoustics applications and is designed to be packaged in an 8 cm/sup 3/ sphere volume with a total mass of 8 grams. In this paper, we describe the accelerometer design, the feedback control design, and several performance enhancements of these micromachined tunneling accelerometers, which include a high resolution of 20 nano-g//spl radic/Hz and a 5 Hz-1.5 kHz bandwidth.

A high-precision, wide-bandwidth micromachined tunneling accelerometer

This review provides a comprehensive survey of noise research in MEMS. Some background on noise and on MEMS is provided. We review noise production mechanisms, and highlight work on the theory and modeling of noise in MEMS. Then noise measurements in the specific types of MEMS are reviewed. Inertial MEMS (accelerometers and angular rate sensors), pressure and acoustic sensors, optical MEMS, RF MEMS, surface acoustic wave devices, flow sensors, and chemical and biological MEMS, as well as data storage devices and magnetic MEMS, are reviewed. We indicate opportunities for additional experimental and computational research on noise in MEMS.

Noise in MEMS

A new high-sensitivity bulk-silicon-micromachined tunneling accelerometer with micro-g resolution has been successfully fabricated and tested at Stanford University. This accelerometer is a prototype intended for underwater acoustics applications and is required to feature micro-g resolution at frequencies between 5 Hz and 1 kHz and can be packaged with circuitry in an 8-cm/sup 3/ volume with a total mass of 8 g. This paper briefly describes the mechanical design of this tunneling accelerometer and focuses on the experiments carried out in our laboratory to test the tunneling transducer as well as on the experimental determination of accelerometer resolution. The exponential relationship between tunneling gap and tunneling current is verified and results in an effective tunneling barrier height of about 0.2 eV. The goal of this paper is to outline the measurements which are necessary to verify that the sensor is actually tunneling and to confirm that the accelerometer performance is consistent with what should be expected from a tunneling accelerometer.

Characterization of a high-sensitivity micromachined tunneling accelerometer with micro-g resolution

In recent years, many researchers have adapted lithography, deposition, and etching techniques from the IC processing community for the fabrication of micromechanical sensors. Many of the signals that these sensors are intended to detect are expressed as forces which stress or deflect the micromechanical structure. As sensors are miniaturized, these forces naturally become smaller, and techniques for detection are required to improve. Many researchers have been engaged in extending MEMS force sensing to the nanometer scale by incorporating new materials and fabrication approaches. This paper will discuss the issues and limitations related to sensing on the nanometer scale and review recent work in this field.

Nanometer-scale force sensing with MEMS devices

A novel micromachined accelerometer based on thermal-bubble technology is proposed and demonstrated in this work Unlike the other techniques, the only moving element in the accelerometer is a small thermal-bubble created by using a high flux heater to vaporize the liquid contained in the micro-chamber The basic physical characteristics including the heat transfer and fluid flow behavior of this sensor have been analyzed and discussed The feasibility and performance of the proposed accelerometer are verified using numerical simulations and demonstrated experimentally using a designed test setup The results conclude that the presented design has better response and higher sensitivity comparing to its counterparts

A novel thermal-bubble-based micromachined accelerometer

In this paper, we discuss the fabrication and initial testing of a bulk micromachined single axis accelerometer. The accelerometer is designed to have a full scale range of and a sensitivity of . Three distinctly different dice are fabricated during the process and are subsequently assembled using an alloy bonding technique. Electrical contacts are made between layers during the bonding operation. The accelerometer is controlled by electrostatic force plates above and below the proof mass. The lower electrode has a dual role. In operation, it provides a necessary control electrode. When not in operation, it is used to immobilize the proof mass.

https://iopscience.iop.org/article/10.1088/0960-1317/6/3/008/pdf

Design and process considerations for a tunneling tip accelerometer

This paper reports the measurement and theoretical analysis of noise in surface micromachined tunneling tip devices. The devices are fabricated using the surface micromachining technology. The bending beams and proof masses are formed by electroplating of nickel and gold. The tips are made by plating metal on the partially etched sacrificial layer. Noise spectra are obtained and compared for different electrode materials and different operating pressures. The results show that 1/f noise dominates in the low frequency region and the 1/f noise level in the vacuum is lower than that in air ambient. A mathematical model is established to simulate the 1/f noise related to surface adsorption-desorption process.

Study of tunneling noise using surface micromachined tunneling tip devices

This paper presents a 30–36 GHz limiter low‐noise amplifier (limiter‐LNA) MMIC for high power and high mobility millimeter‐wave radar systems. The PIN‐diode limiter network and the LNA are codesigned to realize high input‐power handling capability, good small‐signal performance, and small chip area. A two‐state matching capacitor is presented to improve both the input‐power handling capability at the high input‐power level and the input return loss at the small‐signal level. The proposed circuit is fabricated with a combined PIN/0.15‐µm‐GaAs‐pHEMT process. The limiter‐LNA is capable of handling 39 dBm continuous wave (CW) input‐power without failure with only two limiter stages. The measured noise figure is 1.8–2.5 dB, the small‐signal gain is 18.5 ± 0.5 dB, the output power at 1 dB compression point is larger than 11 dBm, and the dc power consumption is 72 mW. The chip area, including testing pads, is only 2.1 mm × 1.0 mm. This limiter‐LNA MMIC is believed to have the highest input‐power handling capability and smallest chip area among limiter‐LNA MMICs at this frequency range reported up to date.

A compact Ka‐band limiter‐low noise amplifier MMIC with high power capability

Lifetime prediction and analysis of AlGaN/GaN HEMT devices under temperature stress

Ultrasensitive accelerometers are needed by NASA for the measurement of orbital drag. We have designed an accelerometer capable of measuring 10-8. In this paper, a method for fabricating a bulk micromachined accelerometer which incorporates a tunneling tip is presented. To meet sensitivity sepcifications, a weak spring and large mass are needed. However, these represent a delicate mechanism and a method of protection is provided by electrostatically clamping the proof mass in a fixed position. The effectiveness of the electrostatic clamp has been measured. It is found that clamping against an acceleration of 200 g is possible with voltages as low as 30 volts.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Jianchao Wang

Papers

Design and process considerations for a tunneling tip accelerometer

Study of tunneling noise using surface micromachined tunneling tip devices

A compact Ka‐band limiter‐low noise amplifier MMIC with high power capability

Lifetime prediction and analysis of AlGaN/GaN HEMT devices under temperature stress

Tunneling Tip Protection for a Bulk Micromachined Accelerometer