Optoelectronic detector with multiple readout nodes and its use thereof

• US 20070176079A1
• Filed: 09/18/2003
• Published: 08/02/2007
• Est. Priority Date: 09/18/2003
• Status: Active Grant

• Current Assignee: Ams Sensors Singapore Pte. Ltd. (Ams-Osram AG)
• Original Assignee: Photonfocus AG (Atlas Copco AB)
• Inventors: Wany, Martin
• Granted Patent: US 7,521,663 B2
• Time in Patent Office: Days
• US Class Current: 250/208.100
• CPC Class Codes: H01L 27/14601 Structural or functional details thereof
• CPC Class Codes: H04N 25/71 Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
• CPC Class Codes: H04N 3/1525 with charge transfer within the image-sensor, e.g. time delay and integration H04N3/1575 takes precedence

Abstract

The present invention discloses an optoelectronic detector for light sensing. The optoelectronic detector has a photosensitive element that converts light into electrons. Efficient collection of these electrons at readout nodes, embedded in the photosensitive element, is required to make correct measurements of light characteristics such as, phase shift and intensity. This collection of electrons is achieved by applying a voltage gradient across an electrode within the optoelectronic detector. The optoelectronic detector can have multiple readout nodes. Further, the present invention discloses methods for detecting intensity and phase shift of impinging light and for suppression of background illumination while detecting the characteristics of light.

Claims

1. An optoelectronic detector comprising:

a. a doped photosensitive substrate;

b. a plurality of doped readout nodes embedded in the doped photosensitive substrate, the photosensitive substrate and the readout nodes being oppositely doped;

c. a plurality of charge-sensing devices, one charge-sensing device being connected to one readout node;

d. a dielectric layer on top of the photosensitive substrate;

e. an electrode on top of the dielectric layer; and

f. a plurality of electrical contact sites fitted on the electrode, one electrical contact site corresponding to one readout node,

wherein the dielectric layer prevents the flow of charges between the electrode and the photosensitive substrate,

whereby a voltage gradient applied across a pair of electrical contact sites generates a constant potential gradient across the corresponding pair of readout nodes.

2. The optoelectronic detector according to claim 1 further comprising a switching unit connected to the electrode, the switching unit changing the voltage gradient on the electrode according to a switching sequence, the switching unit being synchronous to modulation frequency of the light source.

3. The optoelectronic detector according to claim 1 wherein the doped photosensitive substrate is a p-type semiconductor.

4. The optoelectronic detector according to claim 1 wherein the doped photosensitive substrate is an n-type semiconductor.

5. The optoelectronic detector according to claim 1 wherein the charge-sensing device is a current sensing device.

6. The optoelectronic detector according to claim 1 wherein the charge-sensing device is a voltage sensing device.

7. The optoelectronic detector according to claim 1 wherein at least one charge-sensing device is used to drain the electrons collected by the corresponding readout node.

8. The optoelectronic detector according to claim 1 wherein the dielectric layer on top of the photosensitive layer is transparent to light.

9. The optoelectronic detector according to claim 1 wherein the electrode on top of the dielectric layer is transparent to light.

10. A method for suppression of background illumination in modulated light using an optoelectronic detector, the detector having a photosensitive substrate, a plurality of readout nodes and a plurality of means for steering free electrons to one of the readout nodes, the method comprising the steps of:

a. determining a switching sequence, the switching sequence being synchronized with the modulation frequency of the light, the switching sequence comprising periods in which light is present along with background illumination and a period in which only background illumination is present;

b. identifying a readout node corresponding to the period in which only background illumination is present;

c. activating a light source, the activation leading to impingement of modulated light on the photosensitive substrate, the impingement resulting in generation of free electron-hole pairs in the photosensitive substrate;

d. steering free electrons to one of the readout nodes according to the switching sequence, the free electrons being steered to the identified readout node during the period in which only background illumination is present; and

e. draining free electrons collected at the identified readout node.

11. The method according to claim 10 wherein the step of determining a switching sequence comprises the steps of:

a. determining modulation frequency of the modulated light; and

b. determining a time period using the determined modulation frequency.

12. The method according to claim 10 wherein the step of identifying the readout node corresponding to the period in which only background illumination is present comprises the steps of:

a. determining the time period during which light is absent; and

b. determining the readout node to which electrons are steered during the determined time period.

13. The method according to claim 10 wherein the step of steering free electrons to a readout node comprises generating potential gradient across a pair of readout nodes.

14. The method according to claim 13 wherein the step of generating potential gradient comprises the step of applying voltage gradient across the corresponding means for steering free electrons.

15. The method according to claim 10 wherein the step of draining free electrons at a readout node comprises the step of connecting the readout node to a source of reset potential.

16. A method for phase detection of modulated light using an optoelectronic detector with a photosensitive substrate, a plurality of readout nodes embedded in the photosensitive substrate and a plurality of electrical contact sites, each electrical contact site corresponding to one readout node, the method comprising the steps of:

a. determining a switching sequence synchronized with the modulation frequency of the light;

b. identifying a first readout node at which the potential is highest in the first step of the switching sequence;

c. identifying a second readout node at which the potential is highest in the second step of switching sequence;

d. impinging the modulated light on the photosensitive substrate, the impingement resulting in generation of free electrons in the photosensitive substrate, the free electrons being collected at the readout node with higher potential in each step of the switching sequence;

e. generating potential gradient across the first readout node and the second readout node such that the potential at the first readout node is higher in the first step of the switching sequence;

f. inverting potential gradient across the first readout node and the second readout node such that the potential at the second readout node is higher in the second step of switching sequence; and

g. measuring the free electrons collected at the first readout node and the second readout node, the measured values being used to compute the phase shift in the modulated light.

17. The method according to claim 16 wherein determining a switching sequence comprises the steps of:

a. determining modulation frequency of the modulated light; and

b. determining a time period using the determined modulation frequency.

18. The method according to claim 16 wherein the step of generating potential gradient across the first readout node and the second readout node comprises the step of applying voltage gradient across the corresponding electrical contact sites.

19. The method according to claim 16 wherein the step of inverting potential gradient across the first readout node and the second readout node comprises the step of applying negative voltage gradient across the corresponding pair of electrical contact sites.

20. The method according to claim 16 wherein the first step and the second step of the switching sequence are repeated until sufficient charges collect at the first and the second readout nodes.

21. The method according to claim 16 wherein the free electrons collected at the first readout node and the second readout node are measured in the form of voltage.

22. The method according to claim 16 wherein free electrons collected at the first readout node and the second readout node are measured in the form of current.