Transistor with floating gate and electret

• US 7,960,776 B2
• Filed: 09/27/2007
• Issued: 06/14/2011
• Est. Priority Date: 09/27/2006
• Status: Active Grant

• Current Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Inventors: Lee, Chungho, Kan, Edwin Chihchuan, Shen, Nick Yu-Min, Kim, Myongseob
• Primary Examiner(s): Smith; Zandra
• Assistant Examiner(s): Patton; Paul E
• Application Number:
  US11/862,867
• Publication Number:
  US 20080094074A1
• Time in Patent Office: 1,356 Days
• Field of Search: 257314-317
• US Class Current: 257/314
• CPC Class Codes: G01N 27/414 Ion-sensitive or chemical field-effect transistors, i.e. ISFETS or CHEMFETS
• CPC Class Codes: H01L 29/66825 with a floating gate H01L29/6684 takes precedence
• CPC Class Codes: H01L 29/7885 Hot carrier injection from the channel

Abstract

A sensor includes a field effect transistor having a source, drain, a control gate and floating gate, wherein the floating gate has an extended portion extending away from the control gate. A sensing gate is capacitively coupled to the extended portion of the floating gate. A polymer electret sensing coating is electrically coupled to the sensing gate.

Claims

1. A sensor comprising:

a field effect transistor having a source, drain, a control gate and floating gate, wherein the floating gate has an extended portion extending away from the control gate;

a sensing gate capacitively coupled to the extended portion of the floating gate; and

a polymer electret sensing coating electrically coupled to the sensing gate, wherein the polymer electret sensing coating comprises a piezoelectric coating that changes charge conditions on the floating gate responsive to pressure, wherein the piezoelectric coating includes a programmed bias charge.

2. The sensor of claim 1 wherein the piezoelectric coating changes charge conditions on the floating gate responsive to absolute pressure and wherein the control gate is adapted to set a bias point.

3. The sensor of claim 1 wherein the floating gate is charged.

4. The sensor of claim 1 wherein the extended floating gate has an area of approximately 28,800 μ

m² or less.

5. The sensor of claim 1 wherein the piezoelectric coating selected from the group consisting of PZT and PVDF.

6. A sensor comprising:

a field effect transistor having a source and drain formed in or supported by a substrate with a tunnel oxide separating the source and drain, a control gate formed substantially over the tunnel oxide and partially over the source and drain, and a floating gate formed between the tunnel oxide and control gate, wherein the floating gate has an extended portion extending away from the control gate;

a sensing gate capacitively coupled to the extended portion of the floating gate; and

a polymer electret sensing coating electrically coupled to the sensing gate, wherein the polymer electret sensing coating comprises a piezoelectric coating that changes charge conditions on the floating gate responsive to pressure, wherein the piezoelectric coating includes a programmed bias charge.

7. The sensor of claim 6 and further comprising an insulator formed on top of the control gate, extended floating gate and sensing gate, and wherein the oxide has been removed over a portion of the sensing gate to allow contact with the polymer electret sensing coating.

8. The sensor of claim 6 wherein the piezoelectric coating is selected from the group consisting of PZT and PVDF.

9. The sensor of claim 6 and further comprising multiple sensors formed in or supported by the substrate.

10. A method comprising:

exposing an electret sensing coating comprising a piezoelectric coating of a CvMOS transistor sensing gate to pressure, such that the pressure causes a change in charge density in the electret sensing coating;

capacitively coupling the electret sensing coating to an extended portion of a floating gate;

changing a potential on a floating gate of an EEPROM device using a control gate of the CvMOS transistor such that a threshold voltage of the EEPROM device is correlated to the electret charge density; and

programming the electret sensing coating using the control gate.

11. The method of claim 10 wherein programming the electret sensing coating comprises creating a bias charge in the electret sensing coating by applying a high voltage to the control gate.