Capacitive imaging device with active pixels

• US 9,964,575 B2
• Filed: 12/23/2013
• Issued: 05/08/2018
• Est. Priority Date: 11/02/2012
• Status: Expired due to Fees

• Current Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Original Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Inventors: Lu, JengPing
• Primary Examiner(s): Hollington, Jermele M
• Assistant Examiner(s): Fortich, Alvaro
• Application Number:
  US14/139,129
• Publication Number:
  US 20140159746A1
• Time in Patent Office: 1,597 Days
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

An apparatus includes a sensor array with a plurality of active pixels. Each active pixel in the sensor array includes: a three transistor (3T) sensor with a source follower transistor, and a detection diode coupled in series to a parasitic capacitor at a sensing junction. A gate of the source follower transistor amplifier is coupled to the sensing junction. The apparatus includes an insulator layer over the sensor array. The insulator layer provides a variable capacitance to the sensing junctions of underlying active pixels in response to portions of an object being proximate to the insulator layer. The variable capacitance is used to detect an image of the object.

Claims

1. A capacitive image sensor comprising:

a sensor array comprising a plurality of active pixels, each active pixel in the sensor array comprising;

a three-transistor (3T ) sensor comprising a source follower transistor having a gate, wherein the 3T sensor has a charge cycle and a readout cycle, wherein during the charge cycle capacitance builds at the gate of the source follower transistor to establish a first gate voltage; and

an insulator layer over the sensor array, wherein during the reading cycle the insulator layer provides a variable capacitance at the gate of each of the source follower transistors, the variable capacitance establishing a second gate voltage, wherein the difference between the first and second gate voltage is correlative to an object being proximate to the insulator layer, the difference within each active pixel used to detect an image of the object.

2. The capacitive image sensor of claim 1, further comprising an enabling transistor to enable the source follower transistor and a reset transistor to reset the source follower transistor.

3. The capacitive image sensor of claim 2, wherein the enabling transistor enables the charge cycle.

4. The capacitive image sensor of claim 1, further comprising a biasing diode electrically coupled to the gate of the source follower transistor in each active pixel.

5. The capacitive image sensor of claim 1, wherein the object is capable of altering the variable capacitance when it is near the sensor array.

6. The capacitive image sensor of claim 1, wherein the sensor array provides a resolution of at least 500 dpi.

7. The capacitive image sensor of claim 1, wherein the insulator layer comprises a polymer layer, the sensor further comprising a plurality of electrically conductive pads coupling the insulator layer and the gates of the source follower transistor of the underlying pixels.

8. A method for detecting the nearness of an object comprising:

initiating a charge cycle within a plurality of active three-transistor capacitive imaging pixels of a sensor array comprising a plurality of pixels, each active pixel in the sensor array having a source follower transistor having a gate, an enabling transistor to enable the source follower transistor and a reset transistor to reset the source follower transistor;

reading a first voltage at the gate of each of the source follower transistors;

initiating a readout cycle within each of the plurality of active pixels, wherein an insulator layer over the sensor array provides a variable capacitance at the gate of each of the source follower transistors;

reading a second voltage at the gate of each of the source follower transistors, wherein the second voltage is established by the variable capacitance;

determining the difference between the first voltage and the second voltage for each of the plurality of active pixels, the difference correlative to the nearness of the object; and

detecting an image of the object using the difference within each active pixel.

9. The method of claim 8, wherein the array provides a resolution of at least 500 dpi.