Saleh Masoodian

A 2.5 pJ/b Binary Image Sensor as a Pathfinder for Quanta Image Sensors

This paper presents a pathfinder binary image sensor for exploring low-power dissipation needed for future implementation of gigajot single-bit quanta image sensor (QIS) devices. Using a charge-transfer amplifier design in the readout signal chain and pseudostatic clock gating units for row and column addressing, the 1-Mpixel binary image sensor operating at 1000 frames/s dissipates only 20-mW total power consumption, including I/O pads. The gain and analog-to-digital converter stages together dissipate 2.5 pJ/b, successfully paving the way for future gigajot QIS sensor designs.

The Quanta Image Sensor: Every Photon Counts.

The Quanta Image Sensor (QIS) was conceived when contemplating shrinking pixel sizes and storage capacities, and the steady increase in digital processing power. In the single-bit QIS, the output of each field is a binary bit plane, where each bit represents the presence or absence of at least one photoelectron in a photodetector. A series of bit planes is generated through high-speed readout, and a kernel or “cubicle” of bits (x, y, t) is used to create a single output image pixel. The size of the cubicle can be adjusted post-acquisition to optimize image quality. The specialized sub-diffraction-limit photodetectors in the QIS are referred to as “jots” and a QIS may have a gigajot or more, read out at 1000 fps, for a data rate exceeding 1 Tb/s. Basically, we are trying to count photons as they arrive at the sensor. This paper reviews the QIS concept and its imaging characteristics. Recent progress towards realizing the QIS for commercial and scientific purposes is discussed. This includes implementation of a pump-gate jot device in a 65 nm CIS BSI process yielding read noise as low as 0.22 e− r.m.s. and conversion gain as high as 420 µV/e−, power efficient readout electronics, currently as low as 0.4 pJ/b in the same process, creating high dynamic range images from jot data, and understanding the imaging characteristics of single-bit and multi-bit QIS devices. The QIS represents a possible major paradigm shift in image capture.

Quanta Image Sensor (QIS): Early Research Progress

Early research progress in the realization of the Quanta Image Sensor is reported. Simulation of binary data acquisition and image formation was performed. Initial analysis and simulation of a readout signal chain has been performed and bounds on power dissipation established. Photodetector device concepts have been explored using TCAD.

Room temperature 1040fps, 1 megapixel photon-counting image sensor with 1.1um pixel pitch

A 1Mjot single-bit quanta image sensor (QIS) implemented in a stacked backside-illuminated (BSI) process is presented. This is the first work to report a megapixel photon-counting CMOS-type image sensor to the best of our knowledge. A QIS with 1.1μm pitch tapered-pump-gate jots is implemented with cluster-parallel readout, where each cluster of jots is associated with its own dedicated readout electronics stacked under the cluster. Power dissipation is reduced with this cluster readout because of the reduced column bus parasitic capacitance, which is important for the development of 1Gjot arrays. The QIS functions at 1040fps with binary readout and dissipates only 17.6mW, including I/O pads. The readout signal chain uses a fully differential charge-transfer amplifier (CTA) gain stage before a 1b-ADC to achieve an energy/bit FOM of 16.1pJ/b and 6.9pJ/b for the whole sensor and gain stage+ADC, respectively. Analog outputs with on-chip gain are implemented for pixel characterization purposes.

Quanta image sensor: concepts and progress

The QIS was conceived when contemplating shrinking pixel sizes and storage capacities, and the steady increase in digital processing power. In the single-bit QIS, the output of each field is a binary bit plane, where each bit represents the presence or absence of at least one photoelectron in a photodetector. A series of bit planes is generated through high-speed readout, and a kernel or “cubicle” of bits (x,y,t) is used to create a single output image pixel. The size of the cubicle can be adjusted post-acquisition to optimize image quality. The specialized sub-diffraction-limit photodetectors in the QIS are referred to as “jots” and a QIS may have a gigajot or more, read out at 1000 fps, for a data rate exceeding 1Tb/s. Basically, we are trying to count photons as they arrive at the sensor. This paper reviews the Quanta Image Sensor (QIS) concept and its imaging characteristics. Recent progress towards realizing the QIS for commercial and scientific purposes is discussed. The QIS represents a possible major paradigm shift in image capture.

Quanta imaging sensors: achieving single-photon counting without avalanche gain

This paper reports on the state of the art of the Quanta Image Sensor (QIS) being developed by Dartmouth. The QIS is a photon-counting image sensor. Experimental 1Mpixel devices have been implemented in a modified backside-illuminated stacked CMOS image sensor process. Without the use of avalanche multiplicative gain, the sensors have achieved room temperature average read noise of 0.22e- rms (analog readout) permitting photon counting, and over 1000fps readout at under 20mW total power dissipation including pads (single-bit digital readout).

Quanta image sensors: Photon-number-resolving megapixel image sensors at room temperature without avalanche gain

This paper reports on the state of the art of the Quanta Image Sensor (QIS) being developed by Dartmouth. The QIS is a photon-counting image sensor. Experimental 1Mpixel devices have been implemented in a modified backside-illuminated stacked CMOS image sensor process. Without the use of avalanche multiplicative gain, the sensors have achieved room temperature average read noise of 0.22e- rms (analog readout) permitting photon counting, and over 1000fps readout at under 20mW total power dissipation including pads (single-bit digital readout).

Prospects and fundamental limitations of room temperature, non-avalanche, semiconductor photon-counting sensors (Conference Presentation)

This research investigates the fundamental limits and trade-space of quantum semiconductor photodetectors using the Schrödinger equation and the laws of thermodynamics.We envision that, to optimize the metrics of single photon detection, it is critical to maximize the optical absorption in the minimal volume and minimize the carrier transit process simultaneously. Integration of photon management with quantum charge transport/redistribution upon optical excitation can be engineered to maximize the quantum efficiency (QE) and data rate and minimize timing jitter at the same time. Due to the ultra-low capacitance of these quantum devices, even a single photoelectron transfer can induce a notable change in the voltage, enabling non-avalanche single photon detection at room temperature as has been recently demonstrated in Si quanta image sensors (QIS). In this research, uniform III-V quantum dots (QDs) and Si QIS are used as model systems to test the theory experimentally. Based on the fundamental understanding, we also propose proof-of-concept, photon-managed quantum capacitance photodetectors. Built upon the concepts of QIS and single electron transistor (SET), this novel device structure provides a model system to synergistically test the fundamental limits and tradespace predicted by the theory for semiconductor detectors. This project is sponsored under DARPA/AROs DETECT Program: Fundamental Limits of Quantum Semiconductor Photodetectors.