W. Lawrence

Active Pixel Sensors (APSs) in CMOS (complementary metal-oxide-semiconductor) technology are augm... more Active Pixel Sensors (APSs) in CMOS (complementary metal-oxide-semiconductor) technology are augmenting Charge-Coupled Devices (CCDs) as imaging devices and cameras in some demanding optical imaging applications. Radiation Monitoring Devices is investigating the APS concept for nuclear detection applications and has successfully migrated avalanche-photodiode pixel fabrication to a CMOS environment, creating pixel detectors that can be operated with internal gain as proportional detectors. Amplification of the signal within the diode allows identification of events previously hidden within the readout noise of the electronics. Such devices can be used to read out a scintillation crystal, as in SPECT or PET, and as direct-conversion particle detectors. The charge produced by an ionizing particle in the epitaxial layer is collected by an electric field within the diode in each pixel. The monolithic integration of the readout circuitry with the pixel sensors represents an improved design compared to the current hybrid-detector technology that requires wire or bump bonding. In this work, we investigate designs for CMOS avalanche photodiode (APD) detector elements and compare these to typical values for large area devices. We characterize the achievable detector gain and the gain uniformity over the active area. The excess noise in two different pixel structures is compared. The CMOS APD performance is demonstrated by measuring the energy spectra of x-rays from 55 Fe.

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Direct photon-counting scintillation detector readout using an SSPM

by Christopher Stapels and W. Lawrence

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007

Gamma-ray detector technologies, capable of providing adequate energy information, use photomulti... more Gamma-ray detector technologies, capable of providing adequate energy information, use photomultiplier tubes (PMTs) or silicon avalanche photodiodes to detect the light pulse from a scintillation crystal. A new approach to detect the light from scintillation materials is to use an array of small photon counting detectors, or a "detector-on-a-chip" based on a novel "Solid-state Photomultiplier" (SSPM) concept. A CMOS SSPM coupled to a scintillation crystal uses an array of CMOS Geiger photodiode (GPD) pixels to collect light and produce a signal proportional to the energy of the radiation. Each pixel acts as a binary photon detector, but the summed output is an analog representation of the total photon intensity. We have successfully fabricated arrays of GPD pixels in a CMOS environment, which makes possible the production of miniaturized arrays integrated with the detector electronics in a small silicon chip. This detector technology allows for a substantial cost reduction while preserving the energy resolution needed for radiological measurements.

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Solid-State Photomultiplier In CMOS Technology For Gamma-Ray Detection And Imaging Applications

by Christopher Stapels and W. Lawrence

IEEE Nuclear Science Symposium Conference Record, 2005, 2005

1 -A CMOS solid-state photomultiplier (SSPM) coupled to a scintillation crystal uses an array of ... more 1 -A CMOS solid-state photomultiplier (SSPM) coupled to a scintillation crystal uses an array of CMOS Geiger-mode avalanche photodiode (GPD) pixels to collect light and produce a signal proportional to the energy of the radiation. Each pixel acts as a binary photon detector, but the summed output is an analog representation of the total photon intensity. We have successfully fabricated arrays of GPD pixels in a CMOS environment, which makes possible the production of miniaturized arrays integrated with the detector electronics in a small silicon chip.

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<title>A 16-channel avalanche photodiode detector array for visible and near-infrared flow cytometry</title>

by Christopher Stapels and W. Lawrence

Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues IV, 2006

We report on the development and application of a flow cytometer using a 16-channel avalanche pho... more We report on the development and application of a flow cytometer using a 16-channel avalanche photodiode (APD) linear detector array. The array is configured with a dispersive grating to simultaneously record emission over a broad wavelength range using the 16 APD channels of the linear APD array. The APD detector elements have a peak quantum efficiency of 80% near 900

<title>CMOS Geiger-mode avalanche photodiode detectors for time and intensity resolved measurements</title>

by Christopher Stapels and W. Lawrence

MOEMS and Miniaturized Systems IX, 2010

Geiger-mode avalanche photodiode detectors are produced using standard CMOS fabrication methods. ... more Geiger-mode avalanche photodiode detectors are produced using standard CMOS fabrication methods. We have produced integrated circuits that include the Geiger-mode photodetector and digital signal processing circuits. Our current design includes sixteen photon counting detector elements, with bias control, active quenching circuits, and integrated counters at each pixel. The detectors are used to measure chemiluminescence from horseradish peroxidase conjugated antibodies in sub-microliter samples using an optical waveguide. The detector array has been coupled with an external field programmable gate array (FPGA) to perform multi-channel, all digital, time resolved fluorescence measurements of quantum dot nanoparticles and the pH dependence of the fluorescence lifetime of fluorescein dye.

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<title>Single photon detection using Geiger mode CMOS avalanche photodiodes</title>

by Christopher Stapels and W. Lawrence

Optoelectronic Devices: Physics, Fabrication, and Application II, 2005

ABSTRACT Geiger mode Avalanche Photodiodes fabricated using complementary metal-oxide-semiconduct... more ABSTRACT Geiger mode Avalanche Photodiodes fabricated using complementary metal-oxide-semiconductor (CMOS) fabrication technology combine high sensitivity detectors with pixel-level auxiliary circuitry. Radiation Monitoring Devices has successfully implemented CMOS manufacturing techniques to develop prototype detectors with active diameters ranging from 5 to 60 microns and measured detection efficiencies of up to 60%. CMOS active quenching circuits are included in the pixel layout. The actively quenched pixels have a quenching time less than 30 ns and a maximum count rate greater than 10 MHz. The actively quenched Geiger mode avalanche photodiode (GPD) has linear response at room temperature over six orders of magnitude. When operating in Geiger mode, these GPDs act as single photon-counting detectors that produce a digital output pulse for each photon with no associated read noise. Thermoelectrically cooled detectors have less than 1 Hz dark counts. The detection efficiency, dark count rate, and after-pulsing of two different pixel designs are measured and demonstrate the differences in the device operation. Additional applications for these devices include nuclear imaging and replacement of photomultiplier tubes in dosimeters.