Semiconductor Detector Arrays Research Articles

Prototype AEGIS: A Pixel-Array Readout Circuit for Gamma-Ray Imaging.

Semiconductor detector arrays made of CdTe/CdZnTe are expected to be the main components of future high-performance, clinical nuclear medicine imaging systems. Such systems will require small pixel-pitch and much larger numbers of pixels than are available in current semiconductor-detector cameras. We describe the motivation for developing a new readout integrated circuit, AEGIS, for use in hybrid semiconductor detector arrays, that may help spur the development of future cameras. A basic design for AEGIS is presented together with results of an HSPICE™ simulation of the performance of its unit cell. AEGIS will have a shaper-amplifier unit cell and neighbor pixel readout. Other features include the use of a single input power line with other biases generated on-board, a control register that allows digital control of all thresholds and chip configurations and an output approach that is compatible with list-mode data acquisition. An 8×8 prototype version of AEGIS is currently under development; the full AEGIS will be a 64×64 array with 300 μm pitch.

X-ray tomography systems for observations of the effects of radially sheared electric fields on fluctuations in plasmas

Experimental verification of the effects of radially sheared electric-field (or potential) formation in plasmas is one of the most critical issues to understand the physics basis for plasma confinement improvements. In the GAMMA 10 tandem mirror, recent experimental results show shear formation effects on the suppression of not only coherent drift waves but turbulence-like fluctuations without any coherent phasing relation during the ion-confining potential formation period. Contours of the central-cell soft x-ray brightness show spatially and temporally fluctuated structures during a weak sheared period by the use of the 50 channel microchannel plate system. A new x-ray tomography system is developed for analyzing temporally and spatially resolved plasma behavior in the presence or absence of these shear formation effects in GAMMA 10. The system consists of two 48-channel silicon semiconductor detector arrays with different viewing angles. X-ray energy responses of the new detector arrays along with response uniformity of detector channels have been characterized using synchrotron radiation at the Photon Factory.

Spatially resolved electron cyclotron heated plasmas using novel matrix-type X-ray semiconductor–detector arrays

Temporally and spatially resolved X-ray analyses are carried out by using novel matrix-type X-ray semiconductor detector arrays in the GAMMA 10 tandem mirror. The detector array has seven “matrix columns” for the measurements of plasma X-ray profiles so as to make X-ray tomographic reconstructions. Further, six “matrix rows” having various dead layer thicknesses are fabricated as “unbreakable ultra-thin X-ray absorption filters” for simultaneous analyses of six different X-ray energy ranges. The characteristics of the detector array make it possible to obtain spatially resolved plasma electron temperatures down to a few tens of eV and investigate various magnetohydrodynamic activities during a single-plasma discharge alone. Several applications including investigations of electron energy confinement during a period with central-cell electron cyclotron heatings are made with the novel position sensitive semiconductor arrays.

A proposal for both plasma ion- and electron-temperature diagnostics under simultaneous incidence of particles and x-rays into a semiconductor on the basis of a proposed model for a semiconductor detector response

A method is proposed for obtaining radial profiles of plasma temperatures of both plasma ion (Ti) and electron (Te) simultaneously by the use of a semiconductor detector array. The method is based on our developed particle-response model for a semiconductor detector; in particular, the response theory is constructed for giving the applicability in particle energies ranging down to a kiloelectronvolt. Calculated results from our model are in fairly good agreement with experimental data on the detector response of incident particle beams with energies in the range 100 eV to a few kiloelectronvolts. On the basis of the verification of the proposed model, an idea of the use of a developed semiconductor detector array covered with `reliably unbreakable' ultrathin SiO2 `dead-layer filters' having various nanometre-order thicknesses is applied for simultaneous Ti and Te analyses by using charge-exchange neutral particles and x-rays from plasmas. Radial profiles of Ti and Te are obtained in a single plasma discharge alone, and the data reliability is independently cross-checked by a radial scan of a conventional charge-exchange neutral-particle analyser system as well as a 50-channel microchannel plate x-ray diagnostics system in the GAMMA 10 tandem mirror.

Simultaneous measurements of temporally and spatially resolved ion and electron temperatures using a semiconductor detector array in a single plasma discharge

A method is proposed for obtaining radial profiles of both plasma ion (Ti) and electron temperatures (Te) simultaneously using a semiconductor detector. This method for semiconductor Ti diagnostics is proposed on the basis of an alternative “positive” use of a semiconductor “dead layer” as an energy-analysis filter. Filtering dependence of charge-exchange (cx) neutral particles from plasmas on the thickness on the order of a nanometer-thick SiO2 layer is used for analyzing Ti in the range from hundreds to thousands of electron volts. Even under the circumstances of simultaneous incidence of such particles and x rays along the same lines of sight of a semiconductor detector array, it is found that the different dependence on their penetration lengths and deposition depths in semiconductor materials makes it possible to distinguish cx neutral particles for Ti diagnostics from x rays for Te diagnostics. Experimental verification of this concept of the simultaneous Ti and Te diagnostics is carried out in the GAMMA 10 tandem mirror by the use of a matrix-type semiconductor detector. The detector is characterized in terms of compact formation of six rows with different thicknesses of thin dead layers (SiO2) on its surface. Each row has seven channels (columns) for measuring radiation profiles in the radial direction of plasmas so as to make tomographic reconstructions for attaining the actual emissivity profiles in the plasmas. These various SiO2 layers are proposed to be applied as “unbreakable ultrathin radiation-absorption filters” having various thicknesses to distinguish x rays from neutral particles simultaneously.

A novel method for simultaneous observations of plasma ion and electron temperatures using a semiconductor-detector array

A new method for a simultaneous observation of both plasma ion and electron temperatures is proposed using one semiconductor-detector array alone. This method will provide a new application of semiconductor-detector arrays for monitoring the key parameter set of nuclear-fusion triple product (i.e ., ion temperatures, densities, and confinement time) as well as for clarifying physics mechanisms of energy transport between plasma ions and electrons under various plasma confining conditions. This method is developed on the basis of an alternative “positive” use of a semiconductor “dead layer”; that is, an SiO 2 layer is employed as a reliable ultra-thin energy analysis filter for low-energy charge-exchanged neutral particles from plasmas ranging in ion temperatures from 0.1 to several tens of kilo-electron-volts. Using recent fabrication techniques for the thin and uniform SiO 2 layers of the order of tens to hundreds of angstrom, our computer simulation and its experimental verification show the availability of such semiconductors for distinguishing neutral particles (for ion temperatures) from X-rays (for electron temperatures). These are simultaneously emitted from the plasmas into semiconductor detectors; however, we employ their quite different penetration lengths and the resultant different deposition depths and profiles in semiconductor materials. As a result, their output signals are distinguishable for these two different and fundamental species of plasmas.

Tomographic reconstruction of plasma electron temperature profiles using semiconductor detector arrays in the elliptic transition region and the circular central cell of the GAMMA 10 tandem mirror

Elliptically shaped transition-region plasmas located between circularly shaped central cell and fish-tail shaped anchor-cell plasmas have been observed using X-ray tomography techniques for the first time in the world largest tandem mirror device, GAMMA 10. These three regions are connected through the lines of magnetic forces. Electrons are, therefore, anticipated to move easily through these regions along the magnetic field lines when neither appreciable electron losses into the transverse direction across the magnetic field lines nor the formation of electron transport barrier potentials in the parallel direction are expected. From this viewpoint, comparisons of electron temperature ( T e) profiles in these regions, thus, give information on one of the most critical issues in tandem mirror plasma confinement. The first data on good agreement in T e profiles of the central cell and the transition region have supported this basic and essential concept of tandem mirror confinement. Development of position sensitive semiconductor-detector arrays and an upgraded X-ray tomography algorithm for analysing elliptically shaped transition-region plasmas are also reported.

Simultaneous Measurements of Spatial Profiles of Ion and Electron Temperatures Using a Semiconductor Detector Array

A new method is proposed for obtaining radial profiles of both plasma ion (Ti) and electron temperatures (Te) simultaneously using one semiconductor detector array alone. Furthermore, availability of the new idea of the simultaneous Ti and Te diagnostics is experimentally demonstrated by the use of a small-sized semiconductor detector array. This novel method for semiconductor Ti diagnostics is proposed on the basis of an alternative “positive” use of a semiconductor “dead layer” as an energy-analysis filter. Filtering dependence of charge-exchange neutral particles from plasmas on the thickness on the order of nm thick SiO2 layer is used for analyzing Ti ranging from hundreds to thousands eV. In this report, proof-of-principle plasma experiments for the proposed idea are, at first, demonstrated in the GAMMA 10 tandem mirror to verify the availability of this novel idea of distinguishing and identifying each value of Ti and Te by the use of various thin filtering materials. Furthermore, novel experimental data on radial profiles of Ti and Te are simultaneously observed and analyzed using a semiconductor detector array along with the development of a Monte-Carlo computer simulation code for analyzing interactions between semiconductor materials and incident particles. The radial profiles of Ti and Te obtained from semiconductor detectors by the use of the proposed method are found to be in good agreement with those from a charge-exchange neutral-particle Ti analyzer and a microchannel-plate Te detector. Detailed data and analysis method are represented in the paper.

Gamma-ray imaging using a CdZnTe pixel array and a high-resolution, parallel-hole collimator

The poor performance of current parallel-hole collimators is an impediment to planar high-resolution gamma-ray imaging, even when high-resolution semiconductor detector arrays are available. High-resolution parallel-hole collimators are possible but have not been fabricated because conventional collimator construction techniques severely limit achievable bore size and septal thickness. We describe development and testing of a high-resolution collimator with 4096 260-/spl mu/m square bores and 380 /spl mu/-m pitch, matched to our existing 2.5 cm/spl times/2.5 cm hybrid 64/spl times/64 CdZnTe arrays with multiplexer readout. The collimator is a laminar composite of about 100 layers of W sheets produced by photolithography and has an efficiency of 5/spl times/10/sup -5/. We have demonstrated sub-millimeter spatial resolution at 140 keV in both phantom and animal imaging using this system. We present images of resolved individual vertebrae in the spine of a mouse and lymphatic channels and nodes in a rat. The collimator and semiconductor array could form a compact module for use in a wide variety of gamma-ray imaging systems.

A diagnostic method for both plasma ion and electron temperatures under simultaneous incidence of charge-exchange particles and x rays into a semiconductor detector array

An idea for using semiconductor detectors to simultaneously observe both plasma ion Ti and electron Te temperatures is proposed. The idea is also experimentally verified in tandem-mirror plasma shots. This method is developed on the basis of an alternative “positive” use of a semiconductor “dead layer” as an energy-analysis filter. Filtering dependence of charge-exchange neutral particles from plasmas on the thickness of a thin (on the order of nm thick) SiO2 layer is employed for analyzing Ti in the range from hundreds to thousands of eV. Even under the conditions of simultaneous incidence of such particles and x rays into semiconductor detectors, the different dependence on their penetration lengths and deposition depths in semiconductor materials makes it possible to distinguish particles (for Ti) from x rays (for Te). In this letter, proof-of-principle plasma experiments for the proposed idea are carried out to verify the availability of this concept of distinguishing and identifying each value of Ti and Te by the use of various thin filtering materials prior to the use of thinner dead layers.

Progress in the development of large-area modular 64/spl times/64 CdZnTe imaging arrays for nuclear medicine

Previous efforts by our group have demonstrated the potential of hybrid semiconductor detector arrays for use in gamma-ray imaging applications. In this paper, we describe progress in the development of a prototype imaging system consisting of a 64/spl times/64-pixel CdZnTe detector array mated to a multiplexer readout circuit that was custom designed for our nuclear medicine application. The detector array consists of a 0.15 cm thick slab of CdZnTe which has a 64/spl times/64 array of 380 /spl mu/m square pixel electrodes on one side produced by photolithography; the other side has a continuous electrode biased at -150 V. Electrical connections between the detector electrodes and corresponding multiplexer bump pads are made with indium bump bonds. Although the CdZnTe detector arrays characterized in this paper are room-temperature devices, a slight amount of cooling is necessary to reduce thermally generated dark current in the detectors. Initial tests show that this prototype imager functions well with more than 90% of its pixels operating. The device is an excellent imager; phantom images have a spatial resolution of 1.5 mm, limited by the collimator bore.

Development of a 64 × 64 CdZnTe array and associated readout integrated circuit for use in nuclear medicine

Previous work has shown that hybrid semiconductor detector arrays similar to those used in infrared focal-plane arrays are very attractive for use in nuclear medicine and other gamma-ray imaging applications. In this paper, we describe the development of a 64 × 64 readout multiplexer specifically for use in gamma-ray imaging; we also describe the construction of 64 × 64 CdZnTe hybrid detector arrays using the new readout. The readout and detector array are both about one inch square (2.5 cm × 2.5 cm) and have 380 µm pixel pitch. Some initial assembly problems have been resolved by stabilizing the hybrids with epoxy. Preliminary testing results are presented that verify that the 64 × 64 CdZnTe arrays perform as excellent imaging spectrometers.

A novel analysis method for plasma light and soft X-ray tomography data including the three-dimensional diffusion in a semiconductor detector array

The three dimensional diffusion effect in a semiconductor photon detector is directly demonstrated using a spatially distributed charge profile produced by a monochromatic energy beam in a multichannel semiconductor detector. When we substitute the value of the diffusion length obtained by the data on the charge profile and the depletion layer thickness from the data on its capacitance vs applied voltages into our theoretical formula, then the photon energy response data are well fitted by the theory. The effect of this diffusion on the plasma VUV and X-ray data is also demonstrated for obtaining actual plasma data.

Verification of a new three-dimensional charge diffusion effect on the x-ray responses of multichannel semiconductor detector arrays

Verification of a new three-dimensional charge diffusion effect on the x-ray responses of multichannel semiconductor detector arrays

X-ray diagnostic systems in the GAMMA 10 tandem mirror and new x-ray semiconductor-detector responses in the DIII–D tokamak

The energy response of a new semiconductor-detector array in the DIII–D tokamak for plasma x-ray diagnostics is characterized using synchrotron radiation at the Photon Factory (KEK) in Japan. This international cooperation research clarifies its good x-ray response ranging up to about 10 keV. The variations in detector-channel responses are also studied. Furthermore, new aluminum-coated x-ray semiconductor detectors are designed, fabricated, and characterized for the 10-keV-order DIII–D electron studies including the purpose of rf current-drive investigations; a flat response (the quantum efficiency η∼1) up to around 10-keV x rays, and a high efficiency (η≥0.3) even for the 20-keV x rays, are achieved. A wide variety of x-ray detection systems for the x-ray-energy range from a few tens eV to several hundreds keV in the GAMMA 10 tandem mirror is shown; that is, microchannel-plate tomography systems for the 0.01–60-keV x rays, a new ultra-low- energy-sensitive pure-Ge detector (0.2–50 keV), a Si(Li) detector (0.7–150 keV), a conventional pure-Ge detector (1.8–250 keV), and an NaI(Tl) detector (20–750 keV), silicon-surface-barrier detectors, and new semiconductor x-ray detectors for the purpose of the investigations of the effects of potentials on electron behavior in various tandem-mirror regions are represented.

A gamma-ray imager with multiplexer readout for use in ultra-high-resolution brain SPECT

An ultra-high-resolution single photon emission computed tomography (SPECT) system for brain imaging is discussed. The system uses a multiple-pinhole aperture and many modular detectors, each composed of an array of semiconductor detectors read out by a monolithic integrated circuit called a multiplexer (MUX). The modular detectors, being passive integrators can detect individual gamma rays with good energy resolution. They will also have submillimeter spatial resolution and high count-rate capability. The basic concept of these detectors is described, and some of the design considerations for them are reviewed. Some preliminary experiments are reported that demonstrate that semiconductor detectors with multiplexer read-out act as gamma ray detectors. >

Time-resolved angular dependent measurement of triggered light scattering changes in biological suspensions

We describe a photometer for time-resolved measurements of small changes in light scattering suited for suspensions of biological material. The time resolution is 35 mus, the amplitude resolution for bovine rod outer segments is typically delta I/I = 5 X 10(-4) at a scattering angle of = 20 degrees. The use of the apparatus is demonstrated by recording the near infrared scattering of bovine rod outer segments after excitation with flashes of green light. Semiconductor detector arrays are arranged centrosymmetrically around a hemispherical cuvette. The optical characteristics of a hemispherical cuvette and the resulting geometry of cuvette and detection are discussed. Calculations of optimal signal transfer and noise of the detectors led to the following arrangement for each scattering angle: pairs of parallel connected photodiodes are fed into several current-to-voltage converters, whose output voltages are summed up by a summing amplifier. For the test of the device so-called N signals of fresh and liquid N2-frozen and thawed ROS samples were measured at four scattering angles simultaneously. A strong angular dependence (difference scattering curve) of the relative light scattering change is seen for fresh ROS which is transformed into a flat curve by freezing and thawing. It is concluded that the competence of the fresh sample to extend the light-induced local events - presumably rhodopsin conformational changes - into the gross-structural range is terminated by freezing.

Infrared focal planes in intrinsic semiconductors

In this paper, we review the state-of-the-art of intrinsic semiconductor detector arrays and project future areas of development. Infrared focal planes in intrinsic semiconductors offer advantages over extrinsic semiconductor structures in both operating temperature and quantum efficiency. Although the device function of spectral filtering and detection of the incident photon flux is now well understood in intrinsic semiconductors, the function of signal processing has only recently been investigated. As a result, research is directed toward implementation of both hybrid devices, in which the signal processing is accomplished in a silicon multiplexer which is physically and electrically interfaced with an intrinsic semiconductor detector array, and monolithic charge transfer devices in which detection and signal processing are accomplished in the same semiconductor. In the monolithic approach, charge transfer devices have been demonstrated in InSb, and it is likely that similar devices will be realized in InSb related alloys and HgCdTe in the near future. Demonstration of a non-MIS charge transfer design would open up the monolithic approach to the IV-VI alloys. Hybrid focal planes incorporating ≳ 1000 element photodiode arrays have been realized in the III-V and the IV-VI alloys; the detector-multiplexer interface circuit will remain one of the key technical issues in the achievement of a high-performance hybrid focal plane.

Infrared Focal Planes in Intrinsic Semiconductors

In this paper, we review the state-of-the-art of intrinsic semiconductor detector arrays and project future areas of development. Infrared focal planes in intrinsic semiconductors offer advantages over extrinsic semiconductor structures in both operating temperature and quantum efficiency. Although the device function of spectral filtering and detection of the incident photon flux is now well understood in intrinsic semiconductors, the function of signal processing has only recently been investigated. As a result, research is directed toward implementation of both hybrid devices, in which the signal processing is accomplished in a silicon multiplexer which is physically and electrically interfaced with an intrinsic semiconductor detector array, and monolithic charge transfer devices in which detection and signal processing are accomplished in the same semiconductor. In the monolithic approach, charge transfer devices have been demonstrated in InSb, and it is likely that similar devices will be realized in InSb related alloys and HgCdTe in the near future. Demonstration of a non-MIS charge transfer design would open up the monolithic approach to the IV-VI alloys. Hybrid focal planes incorporating /spl lsim/1000 element photodiode arrays have been realized in the III-V and the IV-VI alloys; the detector-multiplexer interface circuit will remain one of the key technical issues in the achievement of a high-performance hybrid focal plane.

Optical sampling transient analyzer system

A 1-GHz optoelectronic sampling transient analyzer system having 10(3) dynamic range has been developed and tested for diagnosing the time-amplitude characteristic of a fast, high voltage, single transient electrical pulse. Sampling rate can be tailored to individual signal analysis requirements. Primary elements are a 350-psec (FWHM) laser, a traveling-wave Kerr cell, a semiconductor detector array with charge collection circuitry, and an analog-to-digital converter with digital data memory.