An automatic tunneling-controlled, micromachined Golay cell has been implemented in a multichip integrated-circuit module. The module is designed specifically for sensing infrared radiation indicative of the concentration of glucose in blood, but its low noise, high gain, and low power consumption also make it attractive for other infrared-sensing applications.
Numerous micromachined sensors based on the use of electronic feedback control to maintain a constant level of quantum-mechanical tunneling of electrons have been reported in NASA Tech Briefs. Particularly relevant was a class of Golay-cell/tunneling-device combinations described in "Micromachined Electron-Tunneling Infrared Detectors" (NPO-18413), in Laser Tech Briefs, Vol. 1, No. 1 (September 1993), page 20.
In the present device, the basic principle described above is exploited to measure the pressure on a membrane of a micromachined Golay cell. A bias voltage is applied across a small gap (about 10 Å wide) between two tunneling electrodes, of which one is the membrane in question coated with metal and the other is a tunneling tip. The bias voltage gives rise to a quantum-mechanical-tunneling current of electrons between these electrodes, and the magnitude of this current depends on the size of the gap.
The distance between the membrane and the tunneling tip is controlled by applying a control voltage to an electrostatic-deflection electrode. The circuit adjusts the control voltage to counteract any deviation of the tunneling current from a preset value and thereby maintain the desired constant gap of about 10 Å. The feedback loop that generates the control voltage includes a long-time-constant integrator, the output of which controls the current through a transistor. The voltage drop of this current through a resistor governs the voltage applied to the electrostatic-deflection electrode. The control voltage is a measure of the force needed to prevent deflection of the membrane from the desired constant gap and is thus a measure of the pressure of gas on the membrane, as affected by absorption of infrared radiation in the gas according to the classical Golay-cell principle.
This work was done by Vardkes Victor Boyadzhyan-Sevak of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Electronic Components and Systems category. In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
Technology Reporting Office JPL Mail Stop 122-116 4800 Oak Grove Drive Pasadena, CA 91109 (818) 354-2240
Refer to NPO-20035, volume and number of this NASA Tech Briefs issue, and the page number.
This Brief includes a Technical Support Package (TSP).
Circuit for automatic tunneling-controlled Golay cell
(reference NPO20035) is currently available for download from the TSP library.
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