J.K. Reynolds

Micromachined silicon tunnel sensor for motion detection

We have used the extreme sensitivity of electron tunneling to variations in electrode separation to construct a novel, compact displacement transducer. Electrostatic forces are used to control the separation between the tunneling electrodes, thereby eliminating the need for piezoelectric actuators. The entire structure is composed of micromachined silicon single crystals, including a folded cantilever spring and a tip. Measurements of displacement sensitivity and noise are reported. This device offers a substantial improvement over conventional technology for applications which require compact, highly sensitive transducers.

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

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.

Wide-bandwidth electromechanical actuators for tunneling displacement transducers

A series of displacement transducers have been demonstrated which are based on the detection of electrons that quantum-mechanically tunnel across a narrow gap between electrodes. These transducers have important applications due to the sensitivity of the tunneling mechanism to sub-/spl Aring/ variations in the electrode gap. In this paper, we describe the recent development of wide-bandwidth electromechanical actuators and simple feedback circuitry which have been adapted for use in tunneling displacement transducers. With these actuators and circuits, we have built tunneling transducers with control bandwidths well in excess of 10 kHz. The design, fabrication, operation, and applications of these actuators are described. >

Novel infrared detector based on a tunneling displacement transducer

The pneumatic infrared detector [M. J. E. Golay, Rev. Sci. Instrum. 18, 347 (1947)] uses thermal expansion of a gas to detect infrared radiation. We have designed a detector based on this principle, but which is constructed entirely from micromachined silicon, and uses an electron tunneling displacement transducer to detect the expansion of the gas. The design, fabrication, and characterization of the first prototype sensor are described. Its sensitivity is competitive with the best available uncooled infrared detectors.

A miniature high-sensitivity broad-band accelerometer based on electron tunneling transducers

Abstract New high sensitivity microsensors have been developed using high-resolution position sensors based on electron tunneling. The design of miniature accelerometers having resolutions approaching 10 −9 g /√Hz is discussed. A new dual-element electron tunneling structure, which overcomes bandwidth limitations of single-element structures, allows design of high sensitivity accelerometers operating in a band from a few Hz to several kHz. A miniature accelerometer based on this structure can thus have application as a sensitive acoustic sensor. Thermal vibration of the proof mass is an extremely important constraint in miniature accelerometers, and can be the dominant limitation on the sensitivity. Thermal noise is analyzed for the suspended masses of the dual-element structure, and compared with electronic noise in the tunneling circuit. With a proof mass of 100 mg, noise analysis predicts limiting resolutions better than 10 −8 g /√Hz between 10 and 100 Hz, and 10 −7 g /√Hz at 1 kHz. Prototype accelerometers have been fabricated by silicon micromachining and tested. A noise resolution of 10 −7 g /√Hz between 4 and 70 Hz and 6 × 10 −7 g /√Hz at 400 Hz is observed in a damped device. The low-frequency responsivity of this device is 100 000 V/ g , decreasing to 1300 V/ g at 600 Hz.

A micromachined silicon electron tunneling sensor

An electron tunneling sensor that takes advantage of the extreme position sensitivity of electron tunneling and the unique properties of micromachined silicon is presented. Anisotropic etchants, such as EDP, are used to create micrometer- and millimeter-scale structures such as single-crystal silicon springs, electrodes, and tunneling tips, which are then incorporated in the sensor. The electrostatic force between a pair of planar electrodes is used to control the separation between the tunneling tip and the surface. The thermal drift, hysteresis, and creep of conventional piezoelectric actuators is thereby avoided. Because the structure is composed entirely of silicon, the usual problems associated with differential thermal expansion in piezoelectric-based tunnel devices are greatly reduced.<<ETX>>

Micromachined tunneling displacement transducers for physical sensors

We have designed and constructed a series of tunneling sensors which take advantage of the extreme position sensitivity of electron tunneling. In these sensors, a tunneling displacement transducer, based on scanning tunneling microscopy principles, is used to detect the signal‐induced motion of a sensor element. Through the use of high‐resonant frequency mechanical elements for the transducer, sensors may be constructed which offer wide bandwidth, and are robust and easily operated. Silicon micromachining may be used to fabricate the transducer elements, allowing integration of sensor and control electronics. Examples of tunneling accelerometers and infrared detectors will be discussed. In each case, the use of the tunneling transducer allows miniaturization of the sensor as well as enhancement of the sensor performance.

Micromachined electron tunneling infrared sensors

The authors describe the development of an improved Golay cell. This sensor is constructed entirely from micromachined silicon components. In this device, a silicon oxynitride (SiO/sub x/N/sub y/) membrane is deflected by the thermal expansion of a small volume of trapped gas. To detect the motion of the membrane, an electron tunneling displacement transducer is used. An improved infrared sensor in which the cantilever was dispensed with altogether, and the rebalance force from the feedback circuit applied to the membrane directly, is described.<<ETX>>

Electron tunnel sensors

We have used the extreme sensitivity of electron tunneling to variations in electrode separation to construct a novel, compact displacement transducer. Electrostatic forces are used to control the separation between the tunneling electrodes, thereby eliminating the need for piezoelectric actuators. The entire structure is composed of micro-machined silicon single crystals, including a folded cantilever spring and a tip. Measurements of displacement sensitivity and noise are reported. Applications of this displacement transducer to the measurement of acceleration and infrared signals are discussed.

Characterization of a high-sensitivity micromachined tunneling accelerometer

We have fabricated successfully and tested a new micromachined tunneling accelerometer. 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. This paper will focus on the experiments carried out in our laboratory to test the tunneling transducer as well as on the experimental determination of accelerometer resolution. 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.