Search

A monolithic solid-state linear sensor array has been designed and fabricated in a 0.35 μm, 3.3 V, thin-oxide digital CMOS process. The sensor arrays are targetted at such instruments and applications as digital streak cameras, 2-D cameras for proton radiography, and fiber-optic array readout. The prototype consists of a I-D linear array of 150 integrated photodiodes, followed by fast analog buffers and on-chip, 150-deep analog frame storage. Frame storage consists of 150 analog sample circuits per pixel, with each sample circuit including an n-channel sample switch, a 0.1 pF double- polysilicon sample capacitor, a reset switch to clear the capacitor, and a multiplexed source-follower readout buffer. Sampling speeds of 400 M-frames/s have been achieved using electrical input signals, and 100 MHz with optical input signals, both with a dynamic range of ∼11.5 bits, rms. Circuit design details are presented, along with the results of electrical measurements and optical experiments with fast pulsed laser light sources at several wavelengths. A set of next-generation concept designs are also presented that aims to include PLL-based clock multiplication for 1 GHz continuous sampling, plus a new real-time trigger circuit technique that examines windowed regions of stored samples to form a sophisticated trigger decision. [ABSTRACT FROM AUTHOR]

Direct-detection CMOS image sensors optimized for charged-particle imaging applications, such as electron microscopy and particle physics, have been designed, fabricated and characterized. Based on standard silicon CMOS Active Pixel Sensor (APS) technology, the sensor arrays uses an 8 to 20 μm epitaxial layer that acts as a thicker sensitive region in the generation and collection of ionization electrons resulting from impinging high-energy particles. A range of optimizations to this technology have been developed via simulation and experimental device design. These include the simulation and measurement of charge collection efficiency versus recombination, effect of diode size and stray capacitance versus signal gain and noise, and the effect of different epitaxial silicon depths and the energy of incident electrons. Results from several experimental devices are presented and compared with simulations, including measurements from two prototypes that systematically and independently vary pixel pitch and diode area. [ABSTRACT FROM AUTHOR]

Abstract: Direct-detection CMOS image sensors optimized for charged-particle imaging applications, such as electron microscopy and particle physics, have been designed, fabricated and characterized. These devices directly image charged particles without reliance on image-degrading hybrid technologies such as the use of scintillating materials. Based on standard CMOS Active Pixel Sensor (APS) technology, the sensor arrays use an 8–20μm thick epitaxial layer that acts as a sensitive region for the generation and collection of ionization electrons resulting from impinging high-energy particles. A range of optimizations to this technology have been developed via simulation and experimental device design. These include the simulation and measurement of charge-collection efficiency vs. recombination, effect of diode area and stray capacitance vs. signal gain and noise, and the effect of different epitaxial silicon depths. Several experimental devices and full-scale prototypes are presented, including two prototypes that systematically and independently vary pixel pitch and diode area, and a complete high-resolution camera for electron microscopy optimized through experiment and simulation. The electron microscope camera has 1×1k2 pixels with a 5μm pixel pitch and an 8μm epitaxial silicon thickness. [Copyright &y& Elsevier]

Abstract: CMOS image sensors optimized for charged particle imaging applications, such as electron microscopy and particle physics, have been designed and characterized. These directly image charged particles without reliance on performance-degrading hybrid technologies such as the use of scintillating materials. Based on standard CMOS active pixel sensor (APS) technology, the sensor arrays uses an 8–20μm epitaxial layer that acts as a thicker sensitive region for the generation and collection of ionization electrons resulting from impinging high-energy particles. This results in a 100% fill factor and a far larger signal per incident electron than a standard CMOS photodiode could provide. A 512×550 pixels prototype has been fabricated and used extensively in an electron microscope, including having been used to take sample images. Temporal noise was measured to be 0.9mV RMS, and the dynamic range was 60dB. Power consumption at 70frames/s is 20mW. The full-width half-maximum of the collected ionization electron distribution was found to be 5.5μm, yielding a spatial resolution of approximately 2.3μm for individual incident electrons, and the modulation transfer function of the sensor at the Nyquist limit is to be 32%. [Copyright &y& Elsevier]

Two CMOS image sensor circuit prototypes equipped with in situ frame storage have been fabricated and tested. Capable of 4-400 M-frames/s and between 66 and 79 dB rms dynamic range, these developments are intended for the capture of fast, brief, transient events with high resolution. Applications include accelerator-based flash radiography such as proton radiography [1]. The first is a small two-dimensional (2-D) prototype in which each pixel includes either a capacitive trans-impedance amplifier or a direct-integration source-follower front end, followed by an array of 64 frame storage sample capacitors and associated readout electronics. The acquisition of either 32 frames using correlated double sampling (CDS) at 4 M-frames/s, or 64 frames without CDS at up to 10.5 M-frames/s (-3 dB), and up to 13 b dynamic range was achieved. The second is a monolithic solid state "streak camera:," a 1-D linear array of 150 photo diodes, with a 150-frame analog storage array. This device reached 400-M-frames/s operation with electrical test inputs, at least 100-M-frames/s operation with optical inputs, and achieves over 11 b of dynamic range. These circuits demonstrate the high performance possible with CMOS sensor circuits containing in situ frame storage. [ABSTRACT FROM AUTHOR]

We describe work that extends three-dimensional (3-D) patterned overlay high-density interconnect (HDI) to high-performance imaging applications. The work was motivated by the rigorous requirements of the multiple-pulse imager for dynamic proton radiography. The optical imager has to provide large (>90%) optical fill factor, high quantum efficiency, 200-ns inter-frame time interval, and storage for >32 frames. In order to accommodate the massively parallel electronics including the signal storage for a large number of frames, it is necessary to provide novel 3-D interconnect and packaging architectures. Recently, a 3-D interconnect technology was successfully demonstrated to assemble a stack of 50 signal-processing chips into a cube. Each chip contained test connections (interconnect continuity only) simulating 160 channels of pixel read-out electronics. Test cube assemblies, based on these mock-up integrated circuits, have been fabricated to explore the feasibility of constructing functional cube arrays. A novel 3D integrated sensor-electronics (mirror-cube) imager architecture is proposed. We also briefly review progress in the custom fast image-processing electronics. [ABSTRACT FROM AUTHOR]

Deals with a study which discussed the design and testing of 2 generations of active pixel sensor chips. Chip configurations; Tests with Fe[sup55]; Effect of radiation.

Abstract: A new high-resolution recording device for transmission electron microscopy (TEM) is urgently needed. Neither film nor CCD cameras are systems that allow for efficient 3-D high-resolution particle reconstruction. We tested an active pixel sensor (APS) array as a replacement device at 200, 300, and 400keV using a JEOL JEM-2000 FX II and a JEM-4000 EX electron microscope. For this experiment, we used an APS prototype with an area of 64×64 pixels of 20μm×20μm pixel pitch. Single-electron events were measured by using very low beam intensity. The histogram of the incident electron energy deposited in the sensor shows a Landau distribution at low energies, as well as unexpected events at higher absorbed energies. After careful study, we concluded that backscattering in the silicon substrate and re-entering the sensitive epitaxial layer a second time with much lower speed caused the unexpected events. Exhaustive simulation experiments confirmed the existence of these back-scattered electrons. For the APS to be usable, the back-scattered electron events must be eliminated, perhaps by thinning the substrate to less than 30μm. By using experimental data taken with an APS chip with a standard silicon substrate (300μm) and adjusting the results to take into account the effect of a thinned silicon substrate (30μm), we found an estimate of the signal-to-noise ratio for a back-thinned detector in the energy range of 200–400keV was about 10:1 and an estimate for the spatial resolution was about 10μm. [Copyright &y& Elsevier]

Abstract: Research has shown that Active Pixel CMOS sensors can detect charged particles. We have been studying whether this process can be used in a collider environment. In particular, we studied the effect of radiation with 55MeV protons. These results show that a fluence of about 2×1012 protons/cm2 reduces the signal by a factor of two while the noise increases by 25%. A measurement 6 months after exposure shows that the silicon lattice naturally repairs itself. Heating the silicon to 100°C reduced the shot noise and increased the collected charge. CMOS sensors have a reduced signal-to-noise ratio per pixel because charge diffuses to neighboring pixels. We have constructed a photogate to see if this structure can collect more charge per pixel. Results show that a photogate does collect charge in fewer pixels, but it takes about 15ms to collect all of the electrons produced by a pulse of light. [Copyright &y& Elsevier]