Mechanical field effect transistor sensor

• US 4,873,871 A
• Filed: 06/17/1988
• Issued: 10/17/1989
• Est. Priority Date: 06/17/1988
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Huhmann, Douglas J., Bai, Monty W.
• Primary Examiner(s): MYRACLE, JERRY
• Application Number:
  US07/207,993
• Time in Patent Office: 487 Days
• Field of Search: 73/777, 73/717, 73/721, 73/862.64, 357/25, 357/26, 357/27
• US Class Current: 73/777
• CPC Class Codes: G01B 7/16 for measuring the deformation in a solid, e.g. by resistance strain gauge
• CPC Class Codes: G01H 11/06 by electric means
• CPC Class Codes: G01L 9/0098 using semiconductor body comprising at least one PN junction as detecting element
• CPC Class Codes: G01P 15/124 by semiconductor devices comprising at least one PN junction, e.g. transistors
• CPC Class Codes: H01L 29/84 controllable by variation of applied mechanical force, e.g. of pressure

Abstract

A mechanical field effect transistor sensor which has a drain and a source on a semiconductor portion, and a moveable gate which causes conduction between the drain and source when the gate is in proximity or touching the semiconductor portion. The gate in its preferred embodiment comprises a cantilever microbeam which allows movement of the gate up or down with respect to the semiconductor portion when a force is applied to the microbeam. The microbeam can be replaced with a diaphragm or a simply supported beam. The gate is coupled to an external voltage source which supplies a voltage to the gate causing the conduction between drain and source. Another embodiment uses a piezoelectric material for the gate which generates a voltage when it is compressed or expanded due to forces caused by changes in acceleration and magnetic fields.

Claims

1. A mechanical field effect transistor sensor comprising:

semiconductor portion means for conducting a current when a surface concentration of electrons of said semiconductor portion means is altered;

deflectable semiconductor means for sensing movement of the sensor;

a bottom portion of said deflectable semiconductor means secured above said semiconductor portion means;

said deflectable semiconductor means deflectable in a vertical direction with respect to said semiconductor portion means;

gate means for altering said surface electron concentration of said semiconductor portion;

said gate means micromachined onto a bottom side of a deflecting portion of said deflectable semiconductor means, and adjacent to said semiconductor portion.

2. A sensor according to claim 1 wherein said semiconductor portion means comprises:

drain means for receiving a current from a primary source;

source means for outputting said current;

semiconductor substrate means for allowing said current to flow from said drain means to said source means when said surface electron concentration is altered; and

said drain means and said source means fixedly secured to a plane of said semiconductor substrate means below said gate means.

3. A sensor according to claim 2 wherein said deflectable semiconductor means further comprises:

end support means for securing said deflectable semiconductor means above said semiconductor means, said end support means secured to said semiconductor means;

said deflecting portion deflecting when the sensor is subject to movement, said deflection proportional to a force caused by said movement;

connector means for connecting said gate means to a voltage source; and

said connector means including a first end coupled to said gate means and a second end coupled to said voltage source.

4. A sensor according to claim 3 wherein said deflectable support means comprises a cantilever microbeam.

5. A sensor according to claim 3 wherein said deflectable support means comprises a diaphragm.

6. A sensor according to claim 1 wherein the sensor is micromachined.

7. A micromachined mechanical field effect transistor sensor comprising:

semiconductor portion means for conducting a current when a surface concentration of electrons of said semiconductor portion means is altered;

deflectable semiconductor means for sensing movement of the sensor;

a bottom portion of said deflectable semiconductor means secured above said semiconductor portion means;

said deflectable semiconductor means deflectable in a vertical direction with respect to said semiconductor portion means;

gate means for altering said surface electron concentration of said semiconductor portion;

said gate means micromachined onto a bottom side of a deflecting portion of said deflectable semiconductor means, and adjacent to said semiconductor portion.

8. A micromachined mechanical field effect transistor sensor according to claim 7 wherein said semiconductor portion means comprises:

drain means for receiving a current from a primary source;

source means for outputting said current;

semiconductor substrate means for allowing said current to flow from said drain means to said source means when said surface electron concentration is altered; and

said drain means and said source means fixedly secured to a plane of said semiconductor substrate means below said gate means.

9. A micromachined mechanical field effect transistor sensor according to claim 7 wherein said deflectable semiconductor means further comprises:

end support means for securing said deflectable semiconductor means above said semiconductor means, said end support means secured to said semiconductor means;

said deflecting portion deflecting when the sensor is subject to movement, said deflection proportional to a force caused by said movement;

connector means for connecting said gate means to a voltage source; and

said connector means including a first end coupled to said gate means and a second end coupled to said voltage source.