Stacked Backside Illuminated SPAD Array
First Claim
1. A back-illuminated single-photon avalanche diode (SPAD) image sensor, comprising:
- a sensor wafer, comprising;
an SPAD region, comprising;
an anode gradient layer comprising a first dopant type;
a cathode region positioned adjacent to a front surface of the SPAD region and comprising a second dopant type; and
an anode avalanche layer positioned over the cathode region and comprising the first dopant type;
wherein;
the cathode region has a first area and the anode avalanche layer has a second area that is less than the first area; and
a dopant concentration of the first dopant type in the anode gradient layer is higher at a back surface of the sensor wafer and lower at a front surface of the anode gradient layer to produce a dopant concentration gradient in the anode gradient layer that guides a photon-generated charge carrier through the anode gradient layer to the anode avalanche layer; and
a circuit wafer positioned below and attached to the sensor wafer.
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Accused Products
Abstract
A back-illuminated single-photon avalanche diode (SPAD) image sensor includes a sensor wafer stacked vertically over a circuit wafer. The sensor wafer includes one or more SPAD regions, with each SPAD region including an anode gradient layer, a cathode region positioned adjacent to a front surface of the SPAD region, and an anode avalanche layer positioned over the cathode region. Each SPAD region is connected to a voltage supply and an output circuit in the circuit wafer through inter-wafer connectors. Deep trench isolation elements are used to provide electrical and optical isolation between SPAD regions.
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Citations
21 Claims
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1. A back-illuminated single-photon avalanche diode (SPAD) image sensor, comprising:
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a sensor wafer, comprising; an SPAD region, comprising; an anode gradient layer comprising a first dopant type; a cathode region positioned adjacent to a front surface of the SPAD region and comprising a second dopant type; and an anode avalanche layer positioned over the cathode region and comprising the first dopant type; wherein; the cathode region has a first area and the anode avalanche layer has a second area that is less than the first area; and a dopant concentration of the first dopant type in the anode gradient layer is higher at a back surface of the sensor wafer and lower at a front surface of the anode gradient layer to produce a dopant concentration gradient in the anode gradient layer that guides a photon-generated charge carrier through the anode gradient layer to the anode avalanche layer; and a circuit wafer positioned below and attached to the sensor wafer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An electronic device, comprising:
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a back-illuminated single-photon avalanche diode (SPAD) image sensor, comprising; a sensor wafer, comprising; a first SPAD region and a second SPAD region adjacent to the first SPAD region, the first and the second SPAD regions each comprising; an anode gradient layer comprising a first dopant; a cathode region comprising a second dopant and adjacent to a front surface of the SPAD region; an anode avalanche layer comprising the first dopant and positioned over the cathode region; and a deep trench isolation region positioned between the first SPAD region and the second SPAD region, the deep trench isolation region extending through a back surface of the sensor wafer; and a circuit wafer attached to the front surface of the sensor wafer; and a processing device operably connected to the back-illuminated SPAD image sensor and configured to; receive output signals from the back-illuminated SPAD image sensor; and determine time-of-flight data based on the output signals. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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20. A back-illuminated single-photon avalanche diode (SPAD) image sensor, comprising:
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a sensor wafer, comprising; an array of SPAD regions, each SPAD region comprising; an anode gradient layer comprising a first dopant type configured in a dopant concentration gradient, the dopant concentration gradient having a higher dopant concentration adjacent to a back surface of the sensor wafer and a lower dopant concentration adjacent to a front surface of the SPAD region; a cathode region comprising a second dopant type and positioned adjacent to the front surface of the SPAD region, the cathode region having a first area; and an anode avalanche layer comprising the first dopant type and positioned over the cathode region, the anode avalanche layer having a second area that is less than the first area; a deep trench isolation region adjacent to each SPAD region in the array of SPAD regions; a light shield positioned over the deep trench isolation region; a passivation layer positioned over an exterior surface of the deep trench isolation regions; and a light reflector positioned below at least a portion of each SPAD region; and a circuit wafer positioned below and attached to the sensor wafer. - View Dependent Claims (21)
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Specification