A Time-Resolved, Low-Noise Single-Photon Image Sensor Fabricated in Deep-Submicron CMOS Technology

Edoardo Charbon, Matthew Fishburn, Marek Gersbach, John Richard Walker
2012
Journal paper

Abstract

We report on the design and characterization of a novel time-resolved image sensor fabricated in a 130 nm CMOS process. Each pixel within the 32x32 pixel array contains a low-noise single-photon detector and a high-precision time-to-digital converter (TDC). The 10-bit TDC exhibits a timing resolution of 119 ps with a timing uniformity across the entire array of less than 2 LSBs. The differential non-linearity (DNL) and integral non-linearity (INL) were measured at +/- 0.4 and +/- 1.2 LSBs, respectively. The pixel array was fabricated with a pitch of 50 mu m in both directions and with a total TDC area of less than 2000 mu m(2). The target application for this sensor is time-resolved imaging, in particular fluorescence lifetime imaging microscopy and 3D imaging. The characterization shows the suitability of the proposed sensor technology for these applications.

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https://infoscience.epfl.ch/record/178410?ln=en

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Imaging techniques based on time-correlated single photon counting (TCSPC), such as fluorescence lifetime imaging microscopy (FLIM), rely on fast single-photon detectors as well as timing electronics in the form of time-to-digital or time-to-analog converters. Conventional systems rely on stand-alone or small arrays (up to 32) of detectors and external timing and memory modules. We recently developed a fully integrated image sensor containing 32x32 pixels and fabricated in a 130 nm CMOS technology. The chip produces an overall data rate of 10Gb/s in terms of time-of-arrival measurements in each pixel. As opposed to conventional single detector FLIM systems, the present system can acquire a full image, albeit at low resolution, without the need of an optical scanning system. As a consequence the complexity of the optical setup is reduced and the acquisition speed is dramatically increased. We show the potential of this new technology by presenting high time resolution (119 ps) TCSPC-FLIM images of pollen grains with acquisition times as low as 69 ms. Furthermore, the low noise (similar to 100 Hz) and high photon detection probability (up to 35%) ensure a good photon economy over the visible spectrum. We believe that this technology will open the way to fast TCSPC-FLIM recordings of transient signals in the bio- and life sciences, such as in neuron signaling.

Spie-Int Soc Optical Engineering, Po Box 10, Bellingham, Wa 98227-0010 Usa2010

A 65k pixel, 150k frames-per-second camera with global gating and micro-lenses suitable for fluorescence lifetime imaging

Claudio Bruschini, Samuel Burri, Edoardo Charbon, François Eric Powolny, Francesco Regazzoni

This paper presents our work on a 65k pixel single-photon avalanche diode (SPAD) based imaging sensor realized in a 0.35 mu m standard CMOS process. At a resolution of 512 by 128 pixels the sensor is read out in 6.4ps to deliver over 150k monochrome frames per second. The individual pixel has a size of 24 mu m(2) and contains the SPAD with a 12T quenching and gating circuitry along with a memory element. The gating signals are distributed across the chip through a balanced tree to minimize the signal skew between the pixels. The array of pixels is row-addressable and data is sent out of the chip on 128 lines in parallel at a frequency of 80MHz. The system is controlled by an FPGA which generates the gating and readout signals and can be used for arbitrary real-time computation on the frames from the sensor. The communication protocol between the camera and a conventional PC is USB2. The active area of the chip is 5% and can be significantly improved with the application of a micro-lens array. A micro-lens array, for use with collimated light, has been designed and its performance is reviewed in the paper. Among other high-speed phenomena the gating circuitry capable of generating illumination periods shorter than 5ns can be used for Fluorescence Lifetime Imaging (FLIM). In order to measure the lifetime of fluorophores excited by a picosecond laser, the sensor's illumination period is synchronized with the excitation laser pulses. A histogram of the photon arrival times relative to the excitation is then constructed by counting the photons arriving during the sensitive time for several positions of the illumination window. The histogram for each pixel is transferred afterwards to a computer where software routines extract the lifetime at each location with an accuracy better than 100ps. We show results for fluorescence lifetime measurements using different fluorophores with lifetimes ranging from 150ps to 5ns.

Spie-Int Soc Optical Engineering2014

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We present the architecture and three applications of the largest resolution image sensor based on single-photon avalanche diodes (SPADs) published to date. The sensor, fabricated in a high-voltage CMOS process, has a resolution of 512 x 128 pixels and a pitch of 24 mu m. The fill-factor of 5% can be increased to 30% with the use of microlenses. For precise control of the exposure and for time-resolved imaging, we use fast global gating signals to define exposure windows as small as 4 ns. The uniformity of the gate edges location is similar to 140 ps (FWHM) over the whole array, while in-pixel digital counting enables frame rates as high as 156 kfps. Currently, our camera is used as a highly sensitive sensor with high temporal resolution, for applications ranging from fluorescence lifetime measurements to fluorescence correlation spectroscopy and generation of true random numbers. (C) 2014 Optical Society of America

Optical Soc Amer2014

A 65k pixel, 150k frames-per-second camera with global gating and micro-lenses suitable for fluorescence lifetime imaging

Claudio Bruschini, Samuel Burri, Edoardo Charbon, François Eric Powolny, Francesco Regazzoni

Spie-Int Soc Optical Engineering2014