Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Patent
1996-07-17
1999-06-08
Oda, Christine K.
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
73862625, G01P 102
Patent
active
059111577
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention is directed to a tunnel effect sensor, particularly an acceleration sensor on silicon.
Modern navigation systems require small, easily manufactured and reliable acceleration sensors with a measuring precision down into the range of one one-millionth of the earth's acceleration. Given other sensors such as, for example, given microphones and pressure sensors as well, it is necessary to determine a temporally variable path difference with extremely high precision given movably attached parts. This is possible upon exploitation of the tunnel effect. In sensors of this type as disclosed, for example, by T. W. Kenny et al. in Applied Physics Letters 58, 100 through 102 (1991) and J.Vac.Sci.Technol. A10 (4), 2114 through 2118 (1992), the tunnel effect between a tip arranged at a movable beam and the silicon substrate is exploited for the measurement.
SUMMARY OF THE INVENTION
An object of the present invention is to specify an easily manufactured tunnel effect sensor whose tunnel tip is protected against destruction with the voltage turned off and that can measure both positive as well as negative forces in sensitivity direction, particularly for monolithic integration with electronic function elements, and to specify an appertaining manufacturing method.
In general terms the present invention is a tunnel effect sensor having a mass part movable at springs that are fashioned in a sensor layer. A tunnel electrode and a cooperating electrode are arranged lying opposite one another in the plane of this sensor layer. Only one of these electrodes is arranged at the mass part. Compensation electrodes are present, these being arranged such that the mass part can be held in a predetermined position by an electrical voltage applied to these compensation electrodes.
Advantageous developments of the present invention are as follows.
The sensor layer is silicon.
The sensor layer is the silicon layer of an SOI substrate
The sensor layer is composed of a conductive material.
The sensor layer is composed of a plurality of layers.
The tunnel electrode is secured to the mass part.
The cooperating electrode is secured to the mass part.
The tunnel electrode and the cooperating electrode are located at an enlarged spacing from one another in the currentless quiescent condition of the mass part. The compensation electrodes are arranged such that, by applying a provided voltage, the mass part can be brought into a position in which the tunnel electrode and the cooperating electrode are located at a spacing from one another provided for a measurement.
Electronic function elements are monolithically integrated The electronic function elements contain a circuit with which such a great electrical voltage is respectively applied to the compensation electrodes that forces of inertia acting on the mass part (4) are electrostatically compensated
The present invention is also a method for the manufacture of a sensor of the type described above whereby the electronic function elements are first produced in the silicon layer of the SOI substrate This silicon layer is then structured as a sensor layer in a region provided for the sensor. The insulator layer of the SOI substrates is then removed in this region at least to an extent required for the mobility of the mass part.
The inventive tunnel effect sensor utilizes the possibility of measurements of the minutest path differences in the range of a few 10.sup.-10 meters using the tunnel effect. The sensor is composed of a mechanically movable structure with a mass part suspended at springs. This structure is attached layer-like over a substrate and is anchored on this substrate. Given acceleration of the substrate, the mass part shifts relative to the substrate due to its inertia. An electrode is connected to the mass part, this electrode residing so close opposite an electrode secured to the substrate that a current flows between these electrodes due to the tunnel effect when a voltage is applied. Given occurrence of an acceleration and, thus
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Applied Physics Letters 58, Micromachined Silicon Tunnel Sensor for Motion Detection, T.W. Kenny et al, Jan. 7, 1991, pp. 100-102.
J. Vac Sci Technol. A10, (4), Electron Tunnel Sensors, T.W. Kenny et al, Jul./Aug. 1992, pp. 2114-2118.
Oda Christine K.
Siemens Aktiengesellschaft
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