Intra-pixel frame storage element, array, and electronic shutter method including speed switch suitable for electronic still camera applications

• US 6,069,376 A
• Filed: 03/26/1998
• Issued: 05/30/2000
• Est. Priority Date: 03/26/1998
• Status: Expired due to Term

• Current Assignee: Foveon, Inc. (Avis Budget Group Incorporated)
• Original Assignee: Foveonics, Inc.
• Inventors: Merrill, Richard B.
• Primary Examiner(s): Whitehead, Jr., Carl
• Assistant Examiner(s): CLARK, SHEILA V
• Application Number:
  US09/048,921
• Time in Patent Office: 796 Days
• Field of Search: 257/291, 257/290, 257/292, 257/294, 257/222, 257/298, 257/223, 257/229, 257/230, 257/231, 257/232, 257/233, 257/228, 438/109, 438/110
• US Class Current: 257/291
• CPC Class Codes: H01L 27/14609 Pixel-elements with integrated switching, control, storage or amplification elements scanning details of imagers (circuitry of solid-state image sensors H04N25/00); circuitry of imagers H04N25/70
• CPC Class Codes: H01L 27/14623 Optical shielding
• CPC Class Codes: H04N 25/53 Control of the integration time
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors
• CPC Class Codes: H04N 25/771 comprising storage means other than floating diffusion

Abstract

A storage pixel sensor disposed on a semiconductor substrate comprises a MOS capacitor storage element having a diffusion terminal and a gate terminal. A speed node is connected to the diffusion terminal and biased at either a first control potential or a second control potential, the first potential selected to keep the MOS capacitor in a state of inversion, the second potential selected to keep the MOS capacitor in a state of depletion. A photodiode has an anode connected to a reference potential and a cathode. A semiconductor reset switch has a first terminal connected to the cathode and a second terminal connected to a reset reference potential. A semiconductor transfer switch has a first terminal connected to the cathode and a second terminal connected to the gate terminal of the capacitive storage element. A semiconductor amplifier has an input connected to the gate terminal of the capacitive storage element and an output. The semiconductor reset switch and the semiconductor transfer switch each have a control element connected to a control circuit for selectively activating the semiconductor reset switch and the semiconductor transfer switch. A light shield is disposed over a portion of the semiconductor substrate including the second terminal of the semiconductor transfer switch to prevent substantially all photons from entering the portion of the semiconductor substrate. Structures are present for preventing substantially all minority carriers generated in the semiconductor substrate from entering the portion of the semiconductor substrate. A plurality of storage pixel sensors are disposed in an array.

Claims

1. A storage pixel sensor disposed on a semiconductor substrate comprising:

a capacitive storage element comprising a MOS capacitor having a diffusion terminal and a gate terminal;

a speed node connected to said diffusion terminal, said speed node biased at either a first control potential or a second control potential, said first control potential selected to keep said MOS capacitor in a state of inversion, and said second control potential selected to keep said MOS capacitor in a state of depletion;

a photodiode having a first terminal and a second terminal, said first terminal connected to a reference potential;

a semiconductor reset switch having a first terminal connected to said second terminal of said photodiode, a second terminal connected to a reset reference potential that reverse biases said photodiode, and a control element connected to a control circuit for selectively activating said semiconductor reset switch;

a semiconductor transfer switch having a first terminal connected to said second terminal of said photodiode, a second terminal connected to said gate terminal of said capacitive storage element, and a control element connected to said control circuit for selectively activating said semiconductor transfer switch;

a semiconductor amplifier having an input and an output, said input connected to said gate terminal of said capacitive storage element;

a light shield disposed over a portion of the semiconductor substrate including said second terminal of said semiconductor transfer switch to prevent substantially all photons from entering said portion of said semiconductor substrate; and

minority carrier rejection means for preventing substantially all minority carriers generated in said semiconductor substrate from entering said second terminal of said semiconductor transfer switch.

2. The storage pixel sensor of claim 1, wherein said portion of said semiconductor substrate further includes said gate terminal of said capacitive storage element and said input of said semiconductor amplifier.

3. The storage pixel sensor of claim 1, further including a semiconductor select switch having an input connected to the output of said amplifier, an output connected to an output bus, and a control element connected to said control circuit.

4. The storage pixel sensor of claim 1 wherein:

said semiconductor substrate is formed from a semiconductor material of a first conductivity type;

said light shield is a portion of a metal layer disposed over said semiconductor substrate;

said semiconductor transfer switch comprises a MOS transistor of a second conductivity type opposite said first conductivity type, said MOS transistor formed in a well of said first conductivity type, said well disposed in said semiconductor substrate, wherein said minority carrier rejection means comprises said well.

5. The storage pixel sensor of claim 1 wherein:

said semiconductor substrate is formed from a semiconductor material of a first conductivity type;

said light shield is a portion of a metal layer disposed over said semiconductor substrate;

said semiconductor transfer switch comprises a MOS transistor of said first conductivity type formed in a well of a second conductivity type opposite said first conductivity type, said well disposed in said semiconductor substrate, wherein said minority carrier rejection means comprises said well.

6. The storage pixel sensor of claim 1 wherein:

said semiconductor substrate is p-type semiconductor substrate;

said light shield is a portion of a metal layer disposed over said semiconductor substrate;

said semiconductor transfer switch comprises an N-Channel MOS transistor formed in a p-well formed in said p-type semiconductor substrate, wherein said minority carrier rejection means comprises said p-well.

7. The storage pixel sensor of claim 1 wherein:

said semiconductor substrate is p-type semiconductor substrate;

said light shield is a portion of a metal layer disposed over said semiconductor substrate;

said semiconductor transfer switch each comprise a P-Channel MOS transistor formed in an n-well formed in said p-type semiconductor substrate, wherein said minority carrier rejection means comprises said n-well.

16. A method for operating a storage pixel sensor of claim 1 including the steps of:

(1) biasing the speed node at either the first control potential or the second control potential;

(2) turning on the transfer switch of the storage pixel sensor for a first time period and turning off said transfer switch at the end of said first time period;

(3) turning on the reset switch of the storage pixel sensor for a reset period occurring during a first portion of said first time period and turning off said reset switch at the end of said first portion of said first time period;

(4) integrating photocurrent in the storage pixel sensor for an integration period occurring during a second portion of said first time period after said reset switch has been turned off, said integration period ending at the end of said first time period;

(5) turning on the reset switch of the storage pixel sensor after the end of said first time period; and

(6) reading an output signal from the amplifier of the storage pixel sensor.

17. A method for operating the storage pixel sensor of claim 1, including the steps of:

(1) biasing the speed node at either the first control potential or the second control potential;

(2) turning on the transfer switch of the storage pixel sensor for a first time period and turning off said transfer switch at the end of said first time period;

(3) turning on the reset switch of the storage pixel sensor for a reset period occurring during a first portion of said first time period and turning off said reset switch at the end of said first portion of said first time period;

(4) integrating photocurrent in the storage pixel sensor for an integration period occurring during a second portion of said first time period after said reset switch has been turned off, said integration period ending at the end of said first time period;

(5) turning on the reset switch of the storage pixel sensor for a reference period after the end of said first time period; and

(6) reading an output signal from the storage pixel sensor, then activating the transfer switch of the storage pixel sensor and reading a reference signal from the storage pixel sensor, then taking the difference between the output signal and the reference signal for the storage pixel sensor.

8. An array of storage pixel sensors disposed on a semiconductor substrate, the array comprising:

a plurality of storage pixel sensors, each storage pixel sensor including;

a capacitive storage element comprising a MOS capacitor having a diffusion terminal and a gate terminal;

a speed node connected to said diffusion terminal, said speed node biased at either a first control potential or a second control potential, said first control potential selected to keep said MOS capacitor in a state of inversion, and said second control potential selected to keep said MOS capacitor in a state of depletion;

a photodiode having a first terminal and a second terminal, said first terminal connected to a reference potential;

a semiconductor reset switch having a first terminal connected to said second terminal of said photodiode, a second terminal connected to a reset reference potential that reverse biases said photodiode, and a control element;

a semiconductor transfer switch having a first terminal connected to said second terminal of said photodiode, a second terminal connected to said gate terminal of said capacitive storage element, and a control element;

a semiconductor amplifier having an input and an output, said input connected to said gate terminal of said capacitive storage element;

a light shield disposed over a portion of the semiconductor substrate including said second terminal of said semiconductor transfer switch to prevent substantially all photons from entering said portion of said semiconductor substrate;

minority carrier rejection means for preventing substantially all minority carriers generated in said semiconductor substrate from entering said second terminal of said semiconductor transfer switch; and

means for generating a reset signal and for coupling said reset signal to the control element of all reset switches in the array;

means for generating a global transfer signal and for coupling said global transfer signal to the control element of all transfer switches in the array; and

a column line for each column in the array, each column line coupled to the outputs of the ones of the semiconductor amplifier associated with that column.

9. The storage pixel sensor of claim 8 further including means for generating a row transfer signal for each row in the array and for coupling the row transfer signal for each row to the control element of all transfer switches associated with that row.

10. The storage pixel sensor of claim 8, wherein said portion of said semiconductor substrate further includes said gate terminal of said capacitive storage element and said input of said semiconductor amplifier.

11. The array of claim 8 wherein each storage pixel sensor further includes a semiconductor select switch having an input connected to the output of said amplifier, an output connected to an output bus, and a control element connected to said control circuit.

12. The array of claim 8 wherein:

said semiconductor substrate is formed from a semiconductor material of a first conductivity type;

said light shield in each storage pixel sensor is a portion of a metal layer disposed over said semiconductor substrate;

said semiconductor transfer switch in each storage pixel sensor comprises a MOS transistor of a second conductivity type opposite said first conductivity type, said MOS transistor formed in a well of said first conductivity type, said well disposed in said semiconductor substrate, wherein said minority carrier rejection means comprises said well.

13. The array of claim 8 wherein:

said semiconductor substrate is formed from a semiconductor material of a first conductivity type;

said light shield in each storage pixel sensor is a portion of a metal layer disposed over said semiconductor substrate;

said semiconductor transfer switch in each storage pixel sensor comprises a MOS transistor of said first conductivity type formed in a well of a second conductivity type opposite said first conductivity type, said well disposed in said semiconductor substrate, wherein said minority carrier rejection means comprises said well.

14. The array of claim 8 wherein:

said semiconductor substrate is p-type semiconductor substrate;

said light shield in each storage pixel sensor is a portion of a metal layer disposed over said semiconductor substrate;

said semiconductor transfer switch in each storage pixel sensor comprises an N-Channel MOS transistor formed in a p-well formed in said p-type semiconductor substrate, wherein said minority carrier rejection means comprises said p-well.

15. The array of claim 8 wherein:

said semiconductor substrate is p-type semiconductor substrate;

said light shield in each storage pixel sensor is a portion of a metal layer disposed over said semiconductor substrate;

said semiconductor transfer switch in each storage pixel sensor comprises a P-Channel MOS transistor formed in an n-well formed in said p-type semiconductor substrate, wherein said minority carrier rejection means comprises said n-well.

18. A method for operating an array of storage pixel sensors of claim 8 arranged in rows, including the steps of:

(1) biasing the speed node of all storage pixel sensors in the array at either the first control potential or the second control potential;

(2) turning on the transfer switches of all storage pixel sensors in the array for a first time period and turning off said transfer switches at the end of said first time period;

(3) turning on the reset switches of all storage pixel sensors in the array for a reset period occurring during a first portion of said first time period and turning off said reset switches at the end of said first portion of said first time period;

(4) integrating photocurrent in all storage pixel sensors in the array for an integration period occurring during a second portion of said first time period after said reset switches have been turned off, said integration period ending at the end of said first time period;

(5) turning on the reset switches of all storage pixel sensors in the array for a reference period after the end of said first time period;

(6) selecting a row of the array and reading an output signal from each storage pixel sensor in the selected row; and

(7) repeating step (6) until output signals for all storage pixel sensors in all rows of the array have been read.

19. A pixel sensor disposed on a semiconductor substrate comprising:

a capacitive element on which photo-generated charge accumulates, said capacitive element having a first terminal on which forms a voltage representative of the amount of light detected, and a second terminal;

a speed control voltage source connected to said second terminal of said capacitive element;

a semiconductor amplifier having an input terminal connected to the first terminal of said capacitive element;

said capacitive element being substantially nonlinear such that the value of the speed control voltage source substantially changes the effective charge-to-voltage conversion gain of the pixel sensor.

20. The pixel sensor of claim 19 wherein:

said capacitive element is a MOS capacitor, said first terminal of said capacitive element comprises a gate terminal of the MOS capacitor, and said second terminal of said capacitive element comprises the diffusion source/drain terminal of the MOS capacitor; and

said speed control voltage source configured to provide first and second control voltages that keep the MOS capacitor operating in inversion and depletion modes respectively.

21. A storage pixel sensor disposed on a semiconductor substrate comprising:

a capacitive storage element comprising a MOS capacitor having a diffusion terminal and a gate terminal capacitor;

a speed node connected to said diffusion terminal, said speed node biased at either a first control potential or a second control potential, said first control potential selected to keep said MOS capacitor in a state of inversion, and said second potential selected to keep said MOS capacitor in a state of depletion;

a photodiode having a first terminal and a second terminal, said first terminal connected to a reference potential;

a semiconductor reset switch having a first terminal connected to said second terminal of said photodiode, a second terminal connected to a reset reference potential that reverse biases said photodiode, and a control element connected to a control circuit for selectively activating said semiconductor reset switch; and

a semiconductor amplifier having an input and an output, said input connected to said gate terminal of said capacitive storage element.

22. The storage pixel sensor of claim 21, further including a semiconductor select switch having an input connected to the output of said amplifier, an output connected to an output bus, and a control element connected to said control circuit.

23. A method for operating a storage pixel sensor of claim 21 including the steps of:

(1) biasing the speed node at either the first control potential or the second control potential;

(2) turning on the reset switch of the storage pixel sensor for a reset period occurring during a first portion of a first time period and turning off said reset switch at the end of said first portion of said first time period;

(3) integrating photocurrent in the storage pixel sensor for an integration period occurring during a second portion of said first time period after said reset switch has been turned off, said integration period ending at the end of said first time period;

(4) turning on the reset switch of the storage pixel sensor after the end of said first time period; and

(5) reading an output signal from the amplifier of the storage pixel sensor.

26. A method for operating an array of storage pixel sensors of claim 23 arranged in rows, including the steps of:

(1) biasing the speed node of all storage pixel sensors in the array at either the first control potential or the second control potential;

(2) turning on the reset switches of all storage pixel sensors in the array for a reset period occurring during a first portion of a first time period and turning off said reset switches at the end of said first portion of said first time period;

(3) integrating photocurrent in all storage pixel sensors in the array for an integration period occurring during a second portion of said first time period after said reset switches have been turned off, said integration period ending at the end of said first time period;

(4) turning on the reset switches of all storage pixel sensors in the array for a reference period after the end of said first time period;

(5) selecting a row of the array and reading an output signal from each storage pixel sensor in the selected row; and

(6) repeating step (5) until output signals for all storage pixel sensors in all rows of the array have been read.

24. An array of storage pixel sensors disposed on a semiconductor substrate, the array comprising:

a plurality of storage pixel sensors, each storage pixel sensor including;

a capacitive storage element comprising a MOS capacitor having a diffusion terminal and a gate terminal;

a speed node connected to said diffusion terminal, said speed node biased at either a first control potential or a second control potential, said first control potential selected to keep said MOS capacitor in a state of inversion, and said second control potential selected to keep said MOS capacitor in a state of depletion;

a photodiode having a first terminal connected to a first potential and a second terminal;

a semiconductor reset switch having a first terminal connected to said second terminal of said photodiode, a second terminal connected to a reset potential that reverse biases said photodiode and a control element;

a semiconductor amplifier having an input connected to said gate terminal of said capacitive storage element and an output;

means for generating a reset signal and for coupling said reset signal to the control elements of all reset switches in the array; and

a column line for each column in the array, each column line coupled to the outputs of the ones of the semiconductor amplifier associated with that column.

25. The array of claim 24 wherein each storage pixel sensor further includes a semiconductor select switch having an input connected to the output of said amplifier, an output connected to an output bus, and a control element connected to said control circuit.