Method and apparatus for backside illuminated image sensors using capacitively coupled readout integrated circuits
First Claim
1. An active pixel image sensor (APS) configured to sense a photon received by a pixel surface, the APS comprising:
- a first integrated circuit (IC) layer having a first back surface coupled to the pixel surface for receiving the photon, a first front surface having a first plate, and an analog device formed between the first back and front surfaces, the analog device coupled to the pixel surface and the first plate;
a second IC layer formed underneath the first IC layer, the second IC layer having second front and back surfaces and a digital device formed between the second front and back surfaces, the second front surface having a second plate configured to be capacitively coupled to the first plate of the first IC layer, the digital device coupled to the second plate of the second front surface; and
a passivation oxide layer coupled between the first and second plates, wherein the first and second plates and the passivation oxide layer form a capacitor between the first and second IC layers.
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Abstract
The images sensor includes a readout circuit capacitatively coupled to a memory circuit. The readout circuit includes: (i) a photon detector to receive a plurality of photons and to provide a charge signal corresponding to the received photons, (ii) a resettable integrator that is reset multiple times over a single exposure time and provides an analog representation of the incident photons during the last integration cycle, and (iii) a comparator that monitors the integrator output and generates a reset pulse when the integrator reaches a built-in threshold value. The memory circuit includes: (i) a receiver circuit that detects the output of the digital driver in the front-end readout circuit via capacitive coupling and generates a digital voltage pulse for each received signal, and (ii) a digital counting memory to count the received pulses to provide a coarse digital representation of how many times the integrator is reset.
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Citations
9 Claims
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1. An active pixel image sensor (APS) configured to sense a photon received by a pixel surface, the APS comprising:
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a first integrated circuit (IC) layer having a first back surface coupled to the pixel surface for receiving the photon, a first front surface having a first plate, and an analog device formed between the first back and front surfaces, the analog device coupled to the pixel surface and the first plate; a second IC layer formed underneath the first IC layer, the second IC layer having second front and back surfaces and a digital device formed between the second front and back surfaces, the second front surface having a second plate configured to be capacitively coupled to the first plate of the first IC layer, the digital device coupled to the second plate of the second front surface; and a passivation oxide layer coupled between the first and second plates, wherein the first and second plates and the passivation oxide layer form a capacitor between the first and second IC layers. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification