Semiconductor Photosensor Research Articles

CALIBRATION OF 122 SENSL MICROFJ-60035 SIPMS AND THE REDUCTION OF OPTICAL CROSS-TALK DUE TO COUPLED LIGHT GUIDES

Recent silicon photomultipliers (SiPMs) boast excellent production quality, eliminating the need for individual breakdown voltage calibration. We present measurements of cross-talk probability and relative gain for 122 SensL MicroFJ-60035-TSV SiPMs. These semiconductor photosensors have replaced photomultiplier tubes in many applications due to their single-photon resolution, insensitivity to magnetic fields, robustness, and cost-effective photon detection at lower voltages. Light guides expand SiPMs' small photosensitive area, and optical coupling reduces cross-talk probability compared to bare sensors at nominal bias voltage, as demonstrated in this study.

High-granularity crystal calorimetry: conceptual designs and first studies

A new concept of high-granularity calorimetry based on crystals has been proposed for future lepton collider experiments, e.g. the Circular Electron Positron Collider (CEPC), with an aim to reach an optimal energy resolution as well as 3D-positioning precision. In this conceptual design, crystals are finely segmented in both transverse and longitudinal directions. Each crystal is optically isolated and read out by a compact semiconductor photosensor (e.g. silicon photomultiplier, SiPM). Simulation models are developed to study the expected performance of the whole calorimeter as well as the readout scheme of a single crystal. Cosmic-ray measurements have been made with a single crystal bar of lead tungstate. First tests with a new front-end electronics chip for the SiPM readout are also presented.

Design of a Depth of Interaction Detector Module for Use in a Magnetic Resonance Imaging System

In this study, we designed a depth of interaction (DOI) detector module for use in a magnetic resonance imaging (MRI) system. The detector uses a semiconductor photosensor that is unaffected by a magnetic field. The detector module consists of two layers of a crystal array that have different light sharing characteristics. To verify the performance of the detector module, simulations of the optical photon transport in the crystal array were performed with a DETECT2000 tool. Various combinations of the parameters, such as the reflector used and the treatment of crystal surfaces, were simulated and the characteristics were evaluated through a reconstructed flood image. In certain combinations of the simulation conditions, all of the crystal pixels could be identified along all directions. Thus, the proposed DOI detector module could extract the three-dimensional gamma ray interaction position from the two-dimensional flood image.

Efficiency and timing resolution of scintillator tiles read out with silicon photomultipliers

Silicon photomultipliers (SiPM) are semiconductor photo sensors that have the potential to replace photomultiplier tubes (PMT) in various fields of application. We present detectors consisting of 30 × 30 × 0.5 cm3 fast plastic scintillator tiles read out with SiPMs. The detectors offer great electronic and mechanical advantages over the classical PMT-scintillator combination. SiPMs are very compact devices that run independent of magnetic fields at low voltages and no light guides between the scintillator and the SiPM are necessary in the presented layouts. Three prototypes, two of which with integrated wavelength shifting fibres, have been tested in a proton beam at the COSY accelerator at Forschungszentrum Jülich. The different layouts are compared in terms of most probable pulse height, detection efficiency and noise behaviour as well as timing resolution. The spatial distributions of these properties across the scintillator surface are presented. The best layout can be operated at a mean efficiency of ϵ̄=99.9 % while sustaining low noise rates in the order of 10 Hz with a timing resolution of less than 3 ns. Both efficiency and timing resolution show good spatial homogeneity.

Photoresponse of an oxide semiconductor photosensor

The authors investigated the photoresponse of a double-layer oxide semiconductor (GaInZnO–InZnO) thin-film transistor (TFT) under illumination, where the photocurrent in the negative gate bias region increased significantly without a negative shift in the threshold voltage. In particular, in the forward gate bias sweep direction (from −VG to +VG), the hysteresis of the transfer curves of the photosensor TFT became pronounced when the negative gate bias and its duration were increased. Additionally, the photocurrent level of the TFT remained almost the same as the level measured using a DC reverse gate bias sweep mode (from +VG to −VG). An analysis of the transfer curves, capacitance–voltage curves, and energy band diagrams indicates that the hysteresis characteristics can be explained by the competing effects of electrical-stress-induced defect generation and the screening of the negative gate bias by doubly positively charged oxygen vacancies depending on the gate bias polarity. In particular, the origin of the photoresponse of the photosensor TFT under illumination was studied intensively by qualitative analysis.

UV Organic Semiconductor Photoconductor with Low Dark Current at High Electric Field

ABSTRACTOrganic semiconductor technology paves the way to low cost lightweight, flexible, printable electronics circuits and sensors. A novel lateral multilayer organic semiconductor photosensor is fabricated using small molecule organic semiconductor. A specialized interface layer is introduced between the metal electrodes and the organic semiconductor layer. The interface layer material is a large band gap and low electronic conductivity material. The use of interface layer limits the charge injection from the electrodes to the organic semiconductor and overall improves the photosensor dark current performance with an additional advantage to apply high voltage for improved collection. This design has low dark current with high photo-to-dark current ratio and can be set to high bias mode of operation.Lateral interdigitated photodetector, with bottom contact Metal Semiconductor Metal (MSM) is fabricated consisting of interface layer and organic semiconductor bilayer. Small molecule organic semiconductor 3,4,9,10 perylenetetracarboxylic bisbenzimidazole (PTCBI) and Copper-Phthalocyanine (CuPc) are used as the active bilayer, where as polyamide forms the interface layer. Current through the sensor is measured in both dark and in light (wavelength 400nm). The dark current density in a 1mm2 photosensor area with 5μm lateral electrode spacing at 10V/μm measured equal to 10-5mA/cm2 and a photocurrent density of 10-3 mA/cm2 under 0.3mW/cm2 incident optical power. The photo to dark current ratio is measured to be equal to ∼103.This photosensor has an application in large area imaging for example portable lightweight detectors. Other applications of this sensor include indirect medial imaging and as a biosensor in UV Spectroscopy study of bacteria cultures.

Feasibility Study of an Axially Extendable Multiplex Cylinder PET

Current clinical PET scanners have a 15-22 cm axial field-of-view (FOV). These scanners image the whole body using six or more bed positions. We designed an axially extendable multiplex cylinder (AEMC) PET scanner to provide high versatility for clinical and research studies using semiconductor photo-sensor based, depth-of-interaction (DOI) detectors. Since silicon-photomultipliers (Si-PMs) have high gain like conventional photomultiplier tubes and a compact design, the Si-PM-based detector is particularly expected to enable various new detector arrangements. The AEMC-PET scanner consists of multiple independent and laminated detector rings using the DOI detectors. The AEMC-PET scanner can extend the axial FOV as each stacked detector ring can be slid sideways. When this PET scanner is used for the four-layer DOI detector, its minimum axial FOV is 24 cm and its maximum crystal thickness is 3 cm. On the other hand, the axial FOV can be extended to 96 cm when laminated detector rings are slid sideways, but the crystal thickness must be 1/4 of 3 cm. In this work, we evaluated performance characteristics of the PET scanner with a variable axial FOV using Monte Carlo simulation. From the simulation of the 180-cm line source, the 96-cm axial FOV was found to have two-fold better sensitivity compared to the 24-cm axial FOV. For extension of the axial FOV, scatter and attenuation of oblique lines-of-response reduced the yield of true coincidences, but effects of scatter and attenuation were small. Conclusive results were obtained showing the 52.8-cm axial FOV yielded an increase in the noise equivalent count rate of approximately 30% relative to the 24-cm axial FOV. We expect the designed AEMC-PET scanner will provide high versatility in applications such as for measuring whole-body tracer uptakes while keeping the continuous axial FOV; as well, the scan time for static images will be reduced for a comparable number of detectors as conventional PET scanners.

Metal Oxide Thin Film Phototransistor for Remote Touch Interactive Displays

The photoresponse characteristics of metal-oxide (MeO) semiconductor photosensors have been studied. Compared to the amorphous-Si-based photo-TFT, the MeO photo-TFT demonstrates superior EQE and responsivity. However, due to its inherent slow recovery to the dark state after the illumination is stopped, a unique sensing scheme suitable for the high-speed array operation is used, yet maintaining a simple array architecture as a solution for large-area interactive displays.

Initial Results of Simultaneous PET/MRI Experiments with an MRI-Compatible Silicon Photomultiplier PET Scanner

The most investigated semiconductor photosensor for MRI-compatible PET detectors is the avalanche photodiode (APD). However, the silicon photomultiplier (SiPM), also called the Geiger-mode APD, is gaining attention in the development of the next generation of PET/MRI systems because the SiPM has much better performance than the APD. We have developed an MRI-compatible PET system based on multichannel SiPM arrays to allow simultaneous PET/MRI. The SiPM PET scanner consists of 12 detector modules with a ring diameter of 13.6 cm and an axial extent of 3.2 cm. In each detector module, 4 multichannel SiPM arrays (with 4 × 4 channels arranged in a 2 × 2 array to yield 8 × 8 channels) were coupled with 20 × 18 Lu(1.9)Gd(0.1)SiO(5):Ce crystals (each crystal is 1.5 × 1.5 × 7 mm) and mounted on a charge division network for multiplexing 64 signals into 4 position signals. Each detector module was enclosed in a shielding box to reduce interference between the PET and MRI scanners, and the temperature inside the box was monitored for correction of the temperature-dependent gain variation of the SiPM. The PET detector signal was routed to the outside of the MRI room and processed with a field programmable gate array-based data acquisition system. MRI compatibility tests and simultaneous PET/MRI acquisitions were performed inside a 3-T clinical MRI system with 4-cm loop receiver coils that were built into the SiPM PET scanner. Interference between the imaging systems was investigated, and phantom and mouse experiments were performed. No radiofrequency interference on the PET signal or degradation in the energy spectrum and flood map was shown during simultaneous PET/MRI. The quality of the MRI scans acquired with and without the operating PET showed only slight degradation. The results of phantom and mouse experiments confirmed the feasibility of this system for simultaneous PET/MRI. Simultaneous PET/MRI was possible with a multichannel SiPM-based PET scanner, with no radiofrequency interference on PET signals or images and only slight degradation of the MRI scans.

Gated three-terminal device architecture to eliminate persistent photoconductivity in oxide semiconductor photosensor arrays

The composition of amorphous oxide semiconductors, which are well known for their optical transparency, can be tailored to enhance their absorption and induce photoconductivity for irradiation with green, and shorter wavelength light. In principle, amorphous oxide semiconductor-based thin-film photoconductors could hence be applied as photosensors. However, their photoconductivity persists for hours after illumination has been removed, which severely degrades the response time and the frame rate of oxide-based sensor arrays. We have solved the problem of persistent photoconductivity (PPC) by developing a gated amorphous oxide semiconductor photo thin-film transistor (photo-TFT) that can provide direct control over the position of the Fermi level in the active layer. Applying a short-duration (10 ns) voltage pulse to these devices induces electron accumulation and accelerates their recombination with ionized oxygen vacancy sites, which are thought to cause PPC. We have integrated these photo-TFTs in a transparent active-matrix photosensor array that can be operated at high frame rates and that has potential applications in contact-free interactive displays.

CMOS Photodetectors Integrated With Plasmonic Color Filters

A single-pixel plasmonic complementary metal oxide semiconductor (CMOS) photo sensor consisting of a plasmonic color filter integrated on a CMOS photodiode was fabricated using electron beam lithography and dry etch. The photocurrent measurement results confirmed the three primary color filtering responses that could be achieved in a single layer of nanostructured aluminium film. Finite-difference time-domain simulation demonstrated a good agreement of the reflection spectra with the measured result. This research can lead to the development of advanced CMOS image sensors with low cost and low crosstalk.

P‐12: Novel Positive‐Intrinsic‐Oxide Semiconductor (P‐I‐OS) Photo Sensor for Flat Panel Displays

AbstractFor the first time, photo sensors employing p‐type Si and IGZO semiconductor (P‐I‐OS) have been fabricated with a sensor dimension of W/L = 1600/5. The IGZO layer was deposited using DC sputtering and replaces the conventional n+‐doped cathode electrode. The P‐I‐OS photo sensor is more sensitive to light with shorter wavelengths, and high to low photo‐current dynamic range is almost constant from −15V to −2.5V of anode bias. The P‐I‐OS photo sensor exhibits dynamic range of 53.3 dB under −5V of anode bias and 10,000 lx of illuminated light intensity

Development of Small-Animal PET Prototype Using Silicon Photomultiplier (SiPM): Initial Results of Phantom and Animal Imaging Studies

Silicon photomultiplier (SiPM; also called a Geiger-mode avalanche photodiode) is a promising semiconductor photosensor in PET and PET/MRI because it is intrinsically MRI-compatible and has internal gain and timing properties comparable to those of a photomultiplier tube. In this study, we have developed a small-animal PET system using SiPMs and lutetium gadolinium oxyorthosilicate (LGSO) crystals and performed physical evaluation and animal imaging studies to show the feasibility of this system. The SiPM PET system consists of 8 detectors, each of which comprises 2 × 6 SiPMs and 4 × 13 LGSO crystals. Each crystal has dimensions of 1.5 × 1.5 × 7 mm. The crystal face-to-face diameter and axial field of view are 6.0 cm and 6.5 mm, respectively. Bias voltage is applied to each SiPM using a finely controlled voltage supply because the gain of the SiPM strongly depends on the supply voltage. The physical characteristics were studied by measuring energy resolution, sensitivity, and spatial resolution. Various mouse and rat images were obtained to study the feasibility of the SiPM PET system in in vivo animal studies. Reconstructed PET images using a maximum-likelihood expectation maximization algorithm were coregistered with animal CT images. All individual LGSO crystals within the detectors were clearly distinguishable in flood images obtained by irradiating the detector using a (22)Na point source. The energy resolution for individual crystals was 25.8% ± 2.6% on average for 511-keV photopeaks. The spatial resolution measured with the (22)Na point source in a warm background was 1.0 mm (2 mm off-center) and 1.4 mm (16 mm off-center) when the maximum-likelihood expectation maximization algorithm was applied. A myocardial (18)F-FDG study in mice and a skeletal (18)F study in rats demonstrated the fine spatial resolution of the scanner. The feasibility of the SiPM PET system was also confirmed in the tumor images of mice using (18)F-FDG and (68)Ga-RGD and in the brain images of rats using (18)F-FDG. These results indicate that it is possible to develop a PET system using a promising semiconductor photosensor, which yielded reasonable PET performance in phantom and animal studies.

A sub-millimeter resolution PET detector module using a multi-pixel photon counter array

A PET block detector module using an array of sub-millimeter lutetium oxyorthosilicate (LSO) crystals read out by an array of surface-mount, semiconductor photosensors has been developed. The detector consists of a LSO array, a custom acrylic light guide, a 3 × 3 multi-pixel photon counter (MPPC) array (S10362-11-050P, Hamamatsu Photonics, Japan) and a readout board with a charge division resistor network. The LSO array consists of 100 crystals, each measuring 0.8 × 0.8 × 3 mm3 and arranged in 0.86 mm pitches. A Monte Carlo simulation was used to aid the design and fabrication of a custom light guide to control distribution of scintillation light over the surface of the MPPC array. The output signals of the nine MPPC are multiplexed by a charge division resistor network to generate four position-encoded analog outputs. Flood image, energy resolution and timing resolution measurements were performed using standard NIM electronics. The linearity of the detector response was investigated using gamma-ray sources of different energies. The 10 × 10 array of 0.8 mm LSO crystals was clearly resolved in the flood image. The average energy resolution and standard deviation were 20.0% full-width at half-maximum (FWHM) and ±5.0%, respectively, at 511 keV. The timing resolution of a single MPPC coupled to a LSO crystal was found to be 857 ps FWHM, and the value for the central region of detector module was 1182 ps FWHM when ±10% energy window was applied. The nonlinear response of a single MPPC when used to read out a single LSO was observed among the corner crystals of the proposed detector module. However, the central region of the detector module exhibits significantly less nonlinearity (6.5% for 511 keV). These results demonstrate that (1) a charge-sharing resistor network can effectively multiplex MPPC signals and reduce the number of output signals without significantly degrading the performance of a PET detector and (2) a custom light guide to permit light sharing among multiple MPPC and to diffuse and direct scintillation light can reduce the nonlinearity of the detector response within the limited dynamic range of a typical MPPC. As a result, the proposed PET detector module has the potential to be refined for use in high-resolution PET insert applications.

Integration of Microcoil Magnetic Manipulation with High-Sensitivity Complementary Metal–Oxide–Semiconductor Photosensor Detection in Bio-Analyses

In this paper, an integration design including a microcoil device and a photodetector with analog-pulse output is proposed for the real-time control and monitoring of magnetic samples or beads of micrometer size. The microcoil array consisting of top metal layers in complementary metal–oxide–semiconductor (CMOS) integrated circuits can successfully manipulate and anchor the magnetic beads by a maximum of 9 G of electromagnetic field when driven by 10 mA. In addition, real-time detection of the location and size of the manipulated samples are demonstrated with an integrated pulse-frequency-modulation (PFM) photosensor array. On the basis of the light intensity received on the sensor plane underneath the microcoils, a bioreaction-induced self-luminance process with a minimal illumination of 5.77×10-5 W/m2 can be successfully identified. This integrated array realized by the CMOS process offers both manipulation and monitoring functions simultaneously, which allows for easier and low-cost parallel bioassay analysis on a single chip.

Geiger-mode avalanche photodiodes for Cherenkov detectors

Semiconductor photo sensors have in comparison with other detectors used in the ring image Cherenkov (RICH) and in the internally reflected Cherenkov light (DIRC) technique, photomultipier tubes and their derivates, a number of advantages: they have high photon detection efficiency ( ∼ 50%), are insensitive to magnetic fields, operate at low voltages and allow a compact, light and robust design. Specially the relatively new Geiger-mode avalanche photodiode (also called silicon photomultiplier) is a promising candidate for a detector of Cherenkov photons. The state of the development and the problems of this device will be described.

Performance evaluation of a digital intraoral imaging device based on the CMOS photosensor array coupled with an integrated X-ray conversion fiber-optic faceplate

As a continuation of our digital X-ray imaging sensor R&D, we have developed a cost-effective, intraoral imaging device based on the complementary-metal–oxide semiconductor (CMOS) photosensor array coupled with an integrated X-ray conversion fiber-optic faceplate. It consists of a commercially available CMOS photosensor of a 35×35 μm 2 pixel size and a 688×910 pixel array dimension, and a high-efficiency columnar CsI(Tl) scintillator of a 90 μm thickness directly deposited on a fiber-optic faceplate of a 6 μm core size and an 1.46 mm thickness with 85/15 core–cladding ratio (NA∼1.0 in air). The fiber-optic faceplate is a highly X-ray attenuating material that minimizes X-ray absorption on the end CMOS photosensor array, thus, minimizing X-ray induced noise at the photosensor array. It uses a high light-output columnar CsI(Tl) scintillator with a peak spectral emission at 545 nm, giving better spatial resolution, but attenuates some of this light due to interfacial and optical attenuation factors. In this paper, we presented the performance analysis of the intraoral imaging device with experimental measurements and acquired X-ray images in terms of modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE).

Modeling and Characterization of the Hydrogenated Amorphous Silicon Metal Insulator Semiconductor Photosensors for Digital Radiography

AbstractBecause of the inherent desired material and technological attributes such as low temperature deposition and high uniformity over large area, the amorphous silicon (a-Si:H) technology has been extended to digital X-ray diagnostic imaging applications. This paper reports on design, fabrication, and characterization of a MIS-type photosensor that is fully process-compatible with the active matrix a-Si:H TFT backplane. We discuss the device operating principles, along with measurement results of the transient dark current, linearity and spectral response.

Considerations for selecting a digital radiography system

Digital detector systems for projection radiography have been available for the past several years and are now becoming clinically common in conjunction with the deployment and implementation of picture archiving and communication systems (PACSs) in radiology and the medical enterprise. A need exists to identify the specific attributes of these detectors, to keep current with technological changes and innovations, and to determine the technology best suited for an intended application. Devices for digital radiography (DR) include computed radiography (CR), charge-coupled devices, two-dimensional and slot-scan linear arrays, complementary metal-oxide semiconductor photosensors, and thin-film-transistor (TFT) two-dimensional flat-panel arrays coupled to either x-ray-to-light scintillators and photodiodes or x-ray-to-charge semiconductor detectors.

Gamma ray detection properties of lutetium aluminate scintillators

A new scintillator material, lutetium orthoaluminate (LuAlO/sub 3/:Ce or LuAP), has been characterized by measuring its light output, scintillation decay time and energy resolution. Successful detection of 511 keV /spl gamma/-rays has been accomplished using LuAP coupled to semiconductor photosensors (silicon avalanche photodiode and silicon p-i-n photodiode). The background spectrum due to the radioactive isotope /sup 176/Lu in LuAP has been measured and characterized, and potential applications of LuAP are addressed.