Static charge dissipation pads for sensors

• US 6,737,329 B2
• Filed: 11/02/2001
• Issued: 05/18/2004
• Est. Priority Date: 12/30/1998
• Status: Expired due to Fees

• Current Assignee: Apple Inc.
• Original Assignee: Upek, Inc. (Apple Inc.)
• Inventors: Raynal, Frederic Denis, Lepert, Arnaud Yves
• Primary Examiner(s): Hu, Shouxiang
• Application Number:
  US10/040,861
• Publication Number:
  US 20020064892A1
• Time in Patent Office: 928 Days
• Field of Search: 438/393-399, 438/238-254, 324/661-662, 324/671, 382/124, 257/532, 257/409, 257/487, 257/488, 257/632
• US Class Current: 438/393
• CPC Class Codes: G06V 40/1329 Protecting the fingerprint sensor against damage caused by the finger

Abstract

A structure and method for dissipating charges comprising an underlying dielectric layer disposed over capacitor plates of sensor circuitry, and a conductive path and passivation layers disposed over the underlying dielectric layer wherein the conductive pad forms an electrically conductive path over at least a portion of the plates and diffuses electrostatic charges at the surface of the integrated circuit.

Claims

1. A method of forming an electrostatic discharge device comprising the steps of:

forming a plurality of conductive plates arranged in pixels each including one or more capacitive sensing electrodes formed by the conductive plates;

forming a protective layer including a dielectric material between and over the plurality of conductive plates, wherein the protective layer electrically isolates the conductive plates, an upper surface of the protective layer serving as a contact surface for a finger forming a capacitor with the capacitive sensing electrodes when a portion of the finger is placed on the contact surface,

wherein the protective layer includes a conductive path disposed therein separated from the conductive plates by a portion of the dielectric material and disposed over at least a portion of at least one of the capacitive sensing electrodes within each pixel, between the portion of the at least one of the capacitive sensing electrodes and the contact surface, the conductive path including openings therethrough over portions of each pixel.

2. The method of claim 1, wherein the conductive path is further defined as comprising a conductive pad disposed over a portion of one of the conductive plates, the conductive pad being connected by a conductive line to ground.

3. A method of forming an electrostatic discharge device comprising the steps of:

forming a dielectric layer over a plurality of conductive plates arranged in pixels each including one or more capacitive sensing electrodes formed by the conductive plates, the dielectric layer electrically isolating the conductive plates, wherein an upper surface of a protective layer including the dielectric layer serves as a contact surface for a finger forming a capacitor with the capacitive sensing electrodes when a portion of the finger is placed on the contact surface; and

forming a conductive pad within the protective layer over at least a portion of one or more of the capacitive sensing electrodes within each pixel and on the dielectric layer, between the portion of the one or more capacitive sensing electrodes and the contact surface, and including openings through the conductive paid over portions of each pixel, wherein the conductive pad dissipates an electrostatic charge in a manner that prevents the electrostatic charge from reaching the plurality of conductive plates.

4. The method of claim 3, wherein the conductive pad is further defined as comprising a central rectangular pad disposed over a portion of one of the conductive plates, the conductive pad being connected by a conductive line to ground.

5. The method of claim 4, rein the central rectangular pad is further defined as comprising an open rectangle connected by the conductive line to ground.

6. The method of claim 4, wherein the conductive pad is further defined as comprising a central closed rectangular pad and open outer rectangle connected by a conductive line.

7. The method of claim 4, wherein the conductive pad is further defined as comprising a combination of a central closed rectangle, an open outer rectangle and a cross.

8. The method of claim 3, wherein the conductive pad is further defined as being generally cross-shaped.

9. The method of claim 3, further comprising the step of:

forming a passivation layer within the protective layer disposed over at least a portion of the dielectric layer and adjacent the conductive pad.

10. The method of claim 3, further comprising the step of:

forming a passivation layer within the protective layer disposed over at least a portion of the dielectric layer and the conductive pad.

11. The method of claim 10, wherein the passivation layer has an optimum thickness to prevent damage to the underlying conductive plates due to use and environment while also allowing an electrostatic charge to dissipate through the conductive pad.

12. The method of claim 10, wherein the passivation layer comprises silicon carbide.

13. The method of claim 10, wherein the passivation layer comprises silicon nitride.

14. A method of forming portion of an integrated circuit for capacitively sensing a fingerprint pattern on a finger, comprising:

forming an array of pairs of capacitive sensing electrodes formed within a single layer and employed for sensing the fingerprint pattern, each of said pairs of capacitive sensing electrodes comprising;

an inner conductive plate forming a central portion; and

an outer conductive plate forming a loop around substantially all of a periphery of the

central portion, the inner and outer conductive plates separated by a gap, wherein each of said pairs of capacitive sensing electrodes forms a single capacitor with a portion of the finger when the finger is placed in proximity to the conductive plates;

forming a protective layer including an insulating material between and over the conductive plates; and

forming a conductive electrostatic discharge pad disposed within the protective layer and overlying at least a portion of at least one of the conductive plates within each of the pairs of capacitive sensing electrodes, the discharge pad separated from the conductive plates by a portion of the insulating material.

15. The method of claim 14, wherein the step of forming the conductive electrostatic discharge pad further comprises:

forming a rectangular portion having an opening therethrough within a central region overlying the conductive plates; and

forming a cross portion within the central region, each arm of the cross portion connecting opposite sides of the rectangular portion.

16. The method of claim 14, wherein the step of forming the conductive electrostatic discharge pad further comprises:

forming a first rectangular portion having an opening therethrough within a central region overlying the conductive plates;

forming a second rectangular portion within the central region and overlying the inner conductive plate; and

forming a conductive line connecting the first and second rectangular portions.

17. The method of claim 14, wherein the step of forming the conductive electrostatic discharge pad further comprises:

forming a first rectangular portion having an opening therethrough within a central region overlying the conductive plates;

forming a second rectangular portion within the central region and overlying the inner conductive plate; and

forming a cross portion within the central region, each arm of the cross portion connecting the first and second rectangular portions.

18. The method of claim 14, wherein the step of forming the electrostatic discharge pad further comprises:

forming the conductive electrostatic discharge pad so that the conductive electrostatic discharge pad does not overlie the gap between the inner and outer conductive plates.

19. The method of claim 14, further comprising:

forming a passivation layer disposed within the protective layer and overlying the insulating material.

20. The method of claim 14, further comprising:

forming a passivation layer disposed within the protective layer and overlying the insulating material and the conductive plates.