CAPACITIVE IMAGING DEVICE WITH ACTIVE PIXELS

• US 20140159746A1
• Filed: 12/23/2013
• Published: 06/12/2014
• Est. Priority Date: 11/02/2012
• Status: Active Grant

• Current Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Original Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Inventors: Lu, JengPing
• Granted Patent: US 9,964,575 B2
• Time in Patent Office: Days
• US Class Current: 324/658
• 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

1-20. -20. (canceled)

21. A capacitive image pixel, 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 a first capacitance builds at the gate of the source follower transistor to establish a first gate voltage and wherein during the readout cycle a second capacitance builds at the gate of the source follower transistor to establish a second gate voltage, wherein the difference between the first and second gate voltage is correlative to the nearness of an object.

22. The capacitive image pixel of claim 21, further comprising an enabling transistor to enable the source follower transistor and a reset transistor to reset the source follower transistor.

23. The capacitive image pixel of claim 22, wherein the enabling transistor enables the charge cycle.

24. The capacitive image pixel of claim 21, further comprising a biasing diode tied to the gate of the source follower transistor.

25. The capacitive image pixel of claim 21, wherein the object is capable of altering the second capacitance when the object is near the 3T sensor.

26. 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.

27. The capacitive image sensor of claim 26, further comprising an enabling transistor to enable the source follower transistor and a reset transistor to reset the source follower transistor.

28. The capacitive image sensor of claim 27, wherein the enabling transistor enables the charge cycle.

29. The capacitive image sensor of claim 26, further comprising a biasing diode electrically coupled to the gate of the source follower transistor in each active pixel.

30. The capacitive image sensor of claim 26, wherein the object is capable of altering the variable capacitance when it is near the sensory array.

31. The capacitive image sensor of claim 26, wherein the sensor array provides a resolution of at least 500 dpi.

32. The capacitive image sensor of claim 26, 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.

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

initiating a charge cycle within a three-transistor capacitive imaging pixel 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 the source follower transistor;

initiating a readout cycle within the pixel;

reading a second voltage at the gate of the source follower transistor; and

determining the difference between the first voltage and the second voltage, the difference correlative to the nearness of the object.

34. The method of claim 33, wherein the three-transistor capacitive imaging pixel comprises an array of three-transistor capacitive imaging pixels.

35. The method of claim 34, detecting an image of the object from the array of pixels.

36. The method of claim 35, wherein the array provides a resolution of at least 500 dpi.