Light-emitting diode arrays with integrated photodetectors formed as a monolithic device and methods and apparatus for using same

• US 5,917,534 A
• Filed: 03/27/1996
• Issued: 06/29/1999
• Est. Priority Date: 06/29/1995
• Status: Expired due to Term

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Rajeswaran, Gopalan
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): NGUYEN, THINH H
• Application Number:
  US08/624,033
• Time in Patent Office: 1,189 Days
• Field of Search: 347/238, 347/236, 347/133, 257/88, 258/578, 258/208.1
• US Class Current: 347/238
• CPC Class Codes: B41J 2/45 using light-emitting diode [LED] or laser arrays

Abstract

A monolithic device comprises an LED chip array that includes photodetectors formed on the device so that each photodetector is associated with a respective LED for detecting light output of the LED. The locations of the photodetectors and the respective rows of bond pads for the LEDs and photodetectors are such as to facilitate connection to associated current driver circuitry. The device is preferably used on an LED printhead. Methods and apparatus are provided for using the device in recording of images. Printheads using such devices allow for determinations of improper operation of the LEDs either in real time or during other times such as interframe per rods. Thus, LED malfunction may be caught promptly without need to stop production to allow a diagnostic photodetector to traverse over the LEDs.

Claims

1. A monolitic device comprising:

(a) a semiconductor substrate;

(b) an array of plural light-emitting elements fabricated in the substrate, the elements being arranged in a row;

(c) a set of respective bond pads and each of the bond pads connected with a respective one of the light-emitting elements for providing respective currents for energizing respective light-emitting elements to emit light, a portion of the light being subsurface light that does not exit the device and another portion of the light being light that does exit the device, the bond pads for adjacent ones of light-emitting elements being located on opposite sides of said row;

(d) a set of respective photodetectors fabricated in the substrate with a respective photodetector being located respectively adjacent each respective light-emitting element;

each respective photodetector being located on an opposite side of said row from a respective bond pad and positioned in sufficiently close proximity to the respective light-emitting element to sense subsurface light emitted by the respective light-emitting element and which subsurface light does not exit the device.

2. The device of claim 1 and wherein there are a plural number N of light emitting elements on the device and a similar number N of first bond pads and a similar number N of second bond pads on the device and wherein the second bond pads are each respectively located further from a respective light-emitting element than a respective one of said first bond pads and the second bond pads are each electronically connected to a respective one of the photodetectors.

3. The device of claim 2 and wherein there are two rows of second bond pads located on the device with the row of light-emitting elements being located between the two rows of second bond pads.

4. The device of claim 1 and wherein there is metallization associated with each photodetector for carrying a current related to light sensed by a respective photodetector and there is a metallization connection electrically connecting each adjacent pair of photodetectors and the metallization connection is located between adjacent light-emitting elements.

5. The device of claim 4 and wherein the metallization connections form a serpentine path about the light-emitting elements and electrically interconnect plural of the photodetectors.

6. The device of claim 5 and wherein a second bond pad is provided on the device and the second bond pad is electrically connected through the metallization connections to plural photodetectors.

7. A monolithic device comprising:

(a) a semiconductor substrate;

(b) an array of plural light-emitting elements fabricated in the substrate, the elements being arranged in a row;

each of light-emitting elements being capable of emitting light, a portion of which exits the device and another portion of which that does not exit the device; and

(c) a set of respective photodetectors fabricated in the substrate with a respective each one of said photodetectors located in sufficiently close proximity to a respective light-emitting element for sensing subsurface light of the respective element which subsurface light does not exit the device.

8. The device of claim 7 and wherein each photodetector is located on an opposite side of said row from a respective photodetector of an adjacent respective light-emitting element.

9. The device of claim 8 and wherein there are a plural number N of light-emitting elements on the device and a similar number N of photodetectors on the device.

10. The device of claim 8 and wherein the photodetectors each include a p-n junction that is of the same composition as a p-n junction that forms a part of each light-emitting element.

11. The device of claim 9 and wherein there is metallization associated with each photodetector for carrying a current related to light sensed by a respective photodetector and there is a metallization connection electrically connecting each adjacent pair of photodetectors and the metallization connection is located between adjacent light-emitting elements.

12. The device of claim 11 and wherein the metallization connections form a serpentine path about the elements and electrically interconnect plural of the photodetectors.

13. The device of claim 12 and wherein a bond pad is provided on the device and the bond pad is electrically connected through the metallization connections to plural photodetectors.

14. The device of claim 13 and wherein the substrate is gallium arsenide.

15. The device of claim 8 in combination with first means for sensing a signal from a photodetector and second means responsive to said signal for changing a parameter related to current to a light-emitting element whose light is sensed by the photodetector.

16. The combination device of claim 15 and wherein said parameter related to current is exposure time.

17. The combination device of claim 16 and wherein said second means changes said parameter related to current in real-time during a recording of a pixel.

18. The combination device of claim 15 and wherein said parameter related to current is amount of current.

19. The combination device of claim 18 and wherein said second means changes said parameter related to current in real-time during a recording of a pixel.

20. A method of diagnosing error in operation of one of plural light-emitting elements on a monolithic device, the device including (a) a semiconductor substrate;

(b) an array of plural light-emitting elements fabricated in the substrate, the elements being arranged in a row; and

(c) a set of respective photodetectors fabricated in the substrate with a respective each one of said photodetectors located in sufficiently close proximity to a respective light-emitting element for sensing light of a respective element which light does not exit the device, said method comprising;

providing data to a driver associated with said one of the light-emitting elements;

in response to said data, enabling said one of said light-emitting elements to emit light, a portion of the light exiting the device and another portion of the light not exiting the device (non-exiting light);

sensing a first signal representing an output parameter by a photodetector and associated with the emission of non-exiting light by said one of said light-emitting elements;

establishing a criterion for determining error between presence of data and sensing of said first signal; and

generating a second signal representing an error in response to comparing of said first signal with said criterion.

21. The method of claim 20 and including the steps of closing a shutter prior to the step of enabling to block light from the light-emitting elements from exposing a photosensitive recording medium.

22. The method of claim 21 and wherein at least one of the light-emitting elements are enabled to record image information on the photosensitive recording medium when the shutter is not closed.

23. The method of claim 22 and wherein diagnosing of error is made during an interframe recording period between periods for recording of image frames on the recording medium.

24. The method of claim 20 and wherein sensing of said first signal is made in real-time during a recording period for recording pixels by said light-emitting elements on a photosensitive recording medium.

25. An apparatus for determining malfunction in operation of one of plural light-emitting elements on a monolithic device, the device including (a) a semiconductor substrate;

(b) an array of plural light-emitting elements fabricated in the substrate, the elements being arranged in a row; and

(c) a set of respective photodetectors fabricated in the substrate with a respective one of said photodetectors located sufficiently proximate each respective light-emitting element for sensing subsurface light of a respective element a portion of which subsurface light does not exit the device (non-exiting light), said apparatus comprising;

means for providing data to a driver associated with said one of said light-emitting elements;

means for enabling, in response to said data, said one of said light-emitting elements;

means for sensing a first signal representing an output parameter of a photodetector which signal is in response to an emission of non-exiting light by said one of said lightemitting elements; and

means, responsive to said first signal, for determining malfunction of said one light-emitting element and generating a second signal representing a malfunction of said one light-emitting element.

26. The apparatus of claim 25 and including a shutter, and means for closing the shutter to block light from the light-emitting elements from exposing a photosensitive recording medium.

27. The apparatus of claim 25 in combination with a photosensitive recording medium and wherein said first signal is sensed in real-time during a recording period for recording pixels by said light-emitting elements on the photosensitive recording medium.

28. A method of monitoring operation of light-emitting elements on a monolithic device, the monolithic device including (a) a semiconductor substrate;

(b) an array of plural light-emitting elements fabricated in the substrate, the elements being arranged in a row; and

(c) a set of respective photodetectors fabricated in the substrate with a respective one of said photodetectors located sufficiently proximate each respective light-emitting element for sensing subsurface light of a respective element which subsurface light does not exit the device, said method comprising;

enabling each of plural ones of said light-emitting elements each with a predetermined current to emit light, a portion of which light exits the device and another portion of which light that does not exit the device (non-exiting light);

sensing signals representing output parameters by respective photodetectors on said device and associated with emission of non-exiting light by each of said ones of said light-emitting elements; and

in response to said signals adjusting an operating parameter to said ones of said light-emitting elements when the sensed signals meet a criterion for adjustment.

29. The method of claim 28 and wherein the operating parameter is exposure duration for recording a pixel by each respective light-emitting element.

30. The method of claim 29 and wherein the operating parameter is amount of current provided to each respective light-emitting element for recording a pixel.