Amorphous Silicon Diodes Research Articles

Amorphous Silicon Diodes as Temperature Sensors in Microwave Thermal Ablation Applications: An Initial Assessment

Amorphous Silicon Diodes as Temperature Sensors in Microwave Thermal Ablation Applications: An Initial Assessment

Investigation of boron-doped hydrogenated silicon films as a thermo-sensing layer for uncooled microbolometer

Boron-doped hydrogenated silicon films are used in thermo-sensing layer in infrared detectors or uncooled microbolometers. Among thermo-sensing materials such as vanadium oxide and amorphous silicon and silicon diodes, amorphous silicon is the most common. Parameters such as the temperature coefficient of resistance (TCR), sheet resistance and 1/f noise are very important for the performance of these devices. One thermo-sensing material in particular, boron-doped hydrogenated silicon (BSi:H), has satisfactory TCR, sheet resistance (Rsheet), and 1/f noise values. The BSi:H films are deposited using radio frequency plasma-enhanced chemical vapor deposition. The dependence of electrical, structural, and chemical properties of the BSi:H films on the plasma parameters is reported. The TCR of the films is 1.0–2.9%/K, Rsheet is 1.2–37.8 MΩ/Υ and crystalline volume fraction is 10.2–68.5%. The properties of the amorphous and mixed-phase are compared. It is found that the 1/f noise of the mixed-phase film is lower than that of the amorphous phase film. These results show that the boron doped mixed-phase silicon films are suitable for use as thermo-sensing layers.

Optoelectronic Properties of Hydrogenated Amorphous Substoichiometric Silicon Carbide with Low Carbon Content Deposited on Semi‐Transparent Boron‐Doped Diamond

Hydrogenated amorphous substoichiometric silicon carbide (a‐Si1−xCx:H, x < 0,1) thin films and diodes with low carbon content are prepared from a mixture of H2, SiH4, and CH4 by plasma‐enhanced chemical vapor deposition at a relatively high temperature of 400 °C on semi‐transparent boron‐doped nanocrystalline diamond (B‐NCD) electrodes with an underlying Ti grid. Vibration spectra indicate that CH4 prevents Si crystallization at elevated deposition temperatures and confirm an increasing carbon content up to x = 0.1 for samples grown with SiH4/CH4 flows up to 1:3. Dark current–voltage characteristics of B‐NCD/a‐Si1−xCx:H diodes show a rectifying ratio of about four orders at ±1 V. However, under white light illumination, an energy conversion efficiency of 4% is limited by a high serial resistivity of the B‐NCD electrode and S‐shaped photocurrent near the open‐circuit voltage.

On-chip LAMP-BART reaction for viral DNA real-time bioluminescence detection

The present paper describes the development of an integrated lab-on-chip, in which viral DNA amplification with real-time on-chip detection is carried out under constant temperature of 65 °C. The lab-on-chip is composed of a disposable 10-μL polydimethylsiloxane reaction chamber which is thermally and optically coupled to a glass substrate that hosts a thin-film metallic resistive heater and thin-film amorphous silicon diodes which act as temperature and radiation sensors. A loop-mediated isothermal amplification (LAMP) technique was optimized to specifically amplify parvovirus B19 DNA and coupled with Bioluminescent Assay in Real Time (BART) technology to provide real-time detection of target DNA. The experimental results demonstrate the ability of the proposed device to discriminate among different concentrations of viral DNA with an excellent agreement with standard off-chip methods.

Multifunctional System-on-Glass for Lab-on-Chip applications

Lab-on-Chip are miniaturized systems able to perform biomolecular analysis in shorter time and with lower reagent consumption than a standard laboratory. Their miniaturization interferes with the multiple functions that the biochemical procedures require. In order to address this issue, our paper presents, for the first time, the integration on a single glass substrate of different thin film technologies in order to develop a multifunctional platform suitable for on-chip thermal treatments and on-chip detection of biomolecules. The proposed System on-Glass hosts thin metal films acting as heating sources; hydrogenated amorphous silicon diodes acting both as temperature sensors to monitor the temperature distribution and photosensors for the on-chip detection and a ground plane ensuring that the heater operation does not affect the photodiode currents.The sequence of the technological steps, the deposition temperatures of the thin films and the parameters of the photolithographic processes have been optimized in order to overcome all the issues of the technological integration.The device has been designed, fabricated and tested for the implementation of DNA amplification through the Polymerase Chain Reaction (PCR) with thermal cycling among three different temperatures on a single site. The glass has been connected to an electronic system that drives the heaters and controls the temperature and light sensors. It has been optically and thermally coupled with another glass hosting a microfluidic network made in polydimethylsiloxane that includes thermally actuated microvalves and a PCR process chamber. The successful DNA amplification has been verified off-chip by using a standard fluorometer.

Parameter determination for device simulations of thin film silicon solar cells by inverse modeling based on temperature and spectrally dependent measurements

Opto-electronic device simulation of thin-film silicon solar cells requires a set of many input parameters for the electronic properties of amorphous and microcrystalline silicon. In this paper, a systematic determination of these is performed by inverse modeling and particle swarm optimization with experimental and simulated current-voltage characteristics of amorphous and microcrystalline silicon pin diodes, both in the dark and under illumination. The parameters are validated by additional experiments and simulations of the temperature-dependent dark current, of spectrally selective illumination, and of the external quantum efficiency of the amorphous and microcrystalline silicon diode, respectively. The validation of the input parameters is complemented by simulation of a tandem solar cell with the amorphous and the microcrystalline silicon input parameters. Simulation and experiment (spectrally dependent current-voltage characteristics and external quantum efficiency) of such a tandem solar cell show good agreement. Sensitivity studies on different sets of input parameters for the inverse modeling process are also presented.

Amorphous Silicon Based Particle Detectors

ABSTRACTRadiation hard monolithic particle sensors can be fabricated by a vertical integration of amorphous silicon particle sensors on top of CMOS readout chip. Two types of such particle sensors are presented here using either thick diodes or microchannel plates. The first type based on amorphous silicon diodes exhibits high spatial resolution due to the short lateral carrier collection. Combination of an amorphous silicon thick diode with microstrip detector geometries permits to achieve micrometer spatial resolution beneficial for high accuracy beam positioning. Microchannel plates based on amorphous silicon were successfully fabricated and multiplication of electrons was observed. This material may solve some of the problems related to conventional microchannel devices. Issues, potential and limits of these detectors are presented and discussed.

Performance and Transient Behavior of Vertically Integrated Thin-film Silicon Sensors.

Vertical integration of amorphous hydrogenated silicon diodes on CMOS readout chips offers several advantages compared to standard CMOS imagers in terms of sensitivity, dynamic range and dark current while at the same time introducing some undesired transient effects leading to image lag. Performance of such sensors is here reported and their transient behaviour is analysed and compared to the one of corresponding amorphous silicon test diodes deposited on glass. The measurements are further compared to simulations for a deeper investigation. The long time constant observed in dark or photocurrent decay is found to be rather independent of the density of defects present in the intrinsic layer of the amorphous silicon diode.

Noise Characteristics and Particle Detection Limits in Diode$+$MTJ Matrix Elements for Biochip Applications

A fully scalable matrix-based magnetoresistive biochip has been recently introduced for the detection of biomolecular recognition events. This work reports results for a 3times3 cells matrix comprising hydrogenated amorphous silicon diodes (PIN and Schottky) and aluminum oxide magnetic tunnel junctions (MTJ). The noise characteristics of the individual thin film diodes (TFD) and the MTJ were analyzed for measuring frequencies from DC to 1 kHz, allowing the detection of single magnetic nanoparticles with 250 nm and 130 nm diameters. For 50 nm particles, and at 1 kHz, minimum number of detectable labels ranges from 20 (Schottky diodes) to 50 (PIN diodes).

Transient Current Behavior of Vertically Integrated Amorphous Silicon Diodes

AbstractMonolithic image sensors based on Thin Film on CMOS (TFC) Technology are becoming more and more attractive as an alternative solution to conventional active pixel sensors (APS). Imager with high sensitivity, high dynamic coupled with low dark current values (10-100 pA/cm2 @ 104 V/cm) have been developed. However, issues such as light-induced degradation and image lag hinder the commercial development of a-Si:H based image sensors. The problem of image lag is caused by residual current due to the release of trapped charges after the switch off of the illumination.In this paper, we present a comprehensive study of the transient behavior of the photocurrent in a-Si:H photodiodes deposited on glass, as well as in corresponding diodes implemented in a TFC image sensor when illumination is switched off or periodically varied. The influence of the pixel architecture for two different cases is also analyzed: One setup reproduces the typical 3 transisor APS pixel architecture behavior, in which the bias voltage of the diode varies with the photogenerated charge while the second setup keeps a constant bias voltage applied to the diode by using a charge integrator.The influence of the light-induced defect creation on the performance of the sensors is also presented and discussed.

Diode/magnetic tunnel junction cell for fully scalable matrix-based biochip

Magnetoresistive biochips have been recently introduced for the detection of biomolecular recognition. In this work, the detection site incorporates a thin-film diode in series with a magnetic tunnel junction (MTJ), leading to a matrix-based biochip that can be easily scaled up to screen large numbers of different target analytes. The fabricated 16×16 cell matrix integrates hydrogenated amorphous silicon (a-Si:H) diodes with aluminum oxide barrier MTJ. Each detection site also includes a U-shaped current line for magnetically assisted target concentration at probe sites. The biochip is being integrated in a portable, credit card size electronics control platform. Detection of 250nm diameter magnetic nanoparticles by one of the matrix cells is demonstrated.

AAPM/RSNA Physics Tutorial for Residents

Recent advances in digital detector technology have paved the way to full-field digital mammography (FFDM) systems. The performance of these systems has evolved to the point where replacement of screen-film mammography (SFM) systems is becoming realistic. Despite some commonality between the two techniques, there are fundamental differences in how images are recorded, displayed, and stored. These differences necessitate an understanding of the principles of detection and the characteristics of digital images. Several approaches have been taken in the development of FFDM systems: (a) slot scanning with a scintillator and a charge-coupled device (CCD) array, (b) a flat-panel scintillator and an amorphous silicon diode array, (c) a flat-panel amorphous selenium array, (d) a tiled scintillator with fiberoptic tapers and a CCD array, and (e) photostimulable phosphor plates (computed radiography). Although the initial cost of an FFDM system is high compared with that of an SFM system, digital mammography has inherent advantages, such as wide dynamic range, reduction in recall rates, potential for reduction in radiation dose, increased patient throughput, postprocessing capability, and digital acquisition. These advantages and the rapidly occurring technologic developments will help establish FFDM as a mainstay of breast evaluation.

Numerical analysis of the spin-dependent dark current in microcrystalline silicon solar cells

We present a detailed analysis of the voltage dependence of dangling bond recombination in microcrystalline silicon p-i-n diodes observed in the forward dark current at room temperature by electrically detected magnetic resonance (EDMR). The EDMR response is numerically simulated with physically reasonable parameters that are well suited to fully describe the electronic behavior of the diodes. A sign reversal as observed for amorphous silicon diodes is predicted at high voltages. The basic mechanism causing the sign reversal is shown to be due to space charge. The high sensitivity of the EDMR response to various material parameters is demonstrated.

Characterization of 13 and 30 μm thick hydrogenated amorphous silicon diodes deposited over CMOS integrated circuits for particle detection application

We present the experimental results obtained with a novel monolithic silicon pixel detector which consists in depositing a n–i–p hydrogenated amorphous silicon (a-Si:H) diode straight above the readout ASIC (this technology is called Thin Film on ASIC, TFA). The characterization has been performed on 13 and 30 μm thick a-Si:H films deposited on top of an ASIC containing a linear array of high-speed low-noise transimpedance amplifiers designed in a 0.25 μm CMOS technology. Experimental results presented have been obtained with a 600 nm pulsed laser. The results of charge collection efficiency and charge collection speed of these structures are discussed.

An amorphous silicon triode rectifier switching device for active-matrix liquid-crystal display

A triode rectifier switching (TRS) device composed of two amorphous silicon (a-Si) diodes and one resistor has been demonstrated experimentally to be a good switching device for active-matrix liquid-crystal display (AMLCD). The output and transfer characteristics of a TRS are very similar to those of an a-Si thin-film transistor. High on/off current ratio (>5/spl times/10/sup 6/) and low off-state leakage currents (<0.4 pA) have been demonstrated with a-Si diodes and a-Si resistor, indicating that the TRS is suitable for high-performance switching devices for AMLCD.

Development of Vertically Integrated Imaging and Particle Sensors

AbstractIntegrated imaging and particle sensors have been developed using thin-film on ASIC technology. For this purpose, hydrogenated amorphous silicon diodes, in various configurations, have been optimized for imaging and direct particle detection. These devices were first deposited on glass substrates and later on CMOS readout chips. With an optimization of the material properties and of the diode, a dark current of 1 pA/cm2 could be achieved on p-i-n structures at reverse bias voltage of 1 V. CMOS imagers, incorporating these optimized diodes were then fabricated and characterized. Very thick diodes (with thicknesses up to 50 μm) were also optimized and deposited on glass and on CMOS readout chips. Particle detectors in TFA technology with 12 and 30 μm a-Si:H n-i-p diodes have been fabricated and characterized using light pulse illumination. Direct detection of single low-energy beta particles has been demonstrated.

Spatial effects on ideality factor of amorphous silicon pin diodes

We analyze dark current-voltage and short-circuit current versus open-circuit voltage measurements of hydrogenated amorphous silicon pin and nip diodes. The ideality factor of ∼1.4 is independent of the thickness of the intrinsic layer, indicating that recombination occurs in the p/i interface region rather than in the bulk. These results can be simulated accurately when the defect-pool model is used. Lateral amorphous silicon diodes with a uniform defect density throughout the intrinsic region have ideality factors, which do depend on the size of the intrinsic region and exceed the theoretical value of 2. We present a model to explain the ideality factor and to verify the results with numerical simulations. Values smaller than 2 are caused by unequal shifts of the quasi-Fermi levels for electrons and holes; values larger than 2 arise when the recombination is spread out over a wide region. In that case the distance between the quasi-Fermi levels is smaller than the applied voltage.

Recombination in Tritiated Amorphous Silicon

ABSTRACTTritiated amorphous silicon was used for the intrinsic layer of a p-i-n hydrogenated amorphous silicon diode. Current versus voltage measurements were carried out on the diode over time under dark and illuminated conditions. There was a decrease in the forward characteristic of the diode when measured under dark conditions and there was a decrease in photovoltaic power. These changes can be explained by the creation of dangling bonds when bonded tritium atoms decay. By annealing the diode at 125 °C, most of its photovoltaic properties could be recovered. It was also found that luminescence could be recovered in tritiated amorphous silicon by thermal annealing.

Vertical integration of a spin dependent tunnel junction with an amorphous Si diode

This work demonstrates integration of magnetic tunneling junctions with hydrogenated amorphous silicon (a-Si:H) diodes. In the finished device 11.4% current change is measured when the junction free layer is switched in an external magnetic field, for 0.86 V applied to the junction-diode series. In the integrated device, the measured individual tunneling magnetoresistance signal is 25.3% at 7 mV bias, demonstrating junction robustness and process compatibility. The junction-diode series is necessary for bit selectivity in magnetic random access memories. Vertical growth of these devices may allow higher density architectures.

Vertical integration of a spin dependent tunnel junction with an amorphous Si diode for MRAM application

This work demonstrates the successful vertical integration of magnetic tunneling junctions with hydrogenated amorphous silicon (a-Si:H) diodes. In the finished device over 11.4% current change was measured when the junction free layer is switched in an external magnetic field, applying 0.86 V to the tunnel junction-diode series. In the integrated device, the TMR signal of the junction measured alone was 25.3% at 7 mV bias, demonstrating junction robustness and process compatibility. The /spl Delta/I/I signal of the junction-diode series was optimized by changing the junction resistance. With the present a-Si:H technology, an RC time constant below 25 ns is calculated, higher than the 2.5 ns estimated for the tunneling junction.