Transistor with floating gate and electret
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.
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 μm 2 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.