Single Photon Avalanche Diode Devices Research Articles

Simulation of photonic crystal enhanced Ge-on-Si single photon avalanche diodes.

Simulations of single photon avalanche diodes (SPADs) based on the Ge-on-Si material platform are presented, highlighting the potential performance enhancement achievable with nano-hole array photonic crystal structures. Such structures can be used to enhance photon absorption and therefore increase single photon detection efficiencies (SPDE). However, there is yet to be a study of these structures in application to Ge-on-Si SPADs to determine if the optical enhancements can be realized as SPDE or to evaluate the change in dark count rate due to the nano-holes that form the photonic crystal. This work establishes an optimization and analysis platform for investigating photonic crystal structures on SPAD devices. Both a direct Ge etch method, and an etched amorphous Si design are compared to a reference device with an optimized anti-reflection coating. Finite difference time domain simulations were used to optimize the photonic crystal parameters for these structures, finding a potential absorption of up to 37.09 % at wavelengths of 1550 nm for a 1 µm absorption layer, compared to 11.33 % for the reference device. Subsequently, TCAD simulations and custom code were used to calculate the effective enhancement to SPAD performance metrics, as a function of material and passivation quality, showing up to 2.41x higher SPDE and 2.57x better noise-equivalent power is achievable provided etched surfaces are sufficiently well passivated.

A Simulation Method for Underwater SPAD Depth Imaging Datasets.

In recent years, underwater imaging and vision technologies have received widespread attention, and the removal of the backward-scattering interference caused by impurities in the water has become a long-term research focus for scholars. With the advent of new single-photon imaging devices, single-photon avalanche diode (SPAD) devices, with high sensitivity and a high depth resolution, have become cutting-edge research tools in the field of underwater imaging. However, the high production costs and small array areas of SPAD devices make it very difficult to conduct underwater SPAD imaging experiments. To address this issue, we propose a fast and effective underwater SPAD data simulation method and develop a denoising network for the removal of backward-scattering interference in underwater SPAD images based on deep learning and simulated data. The experimental results show that the distribution difference between the simulated and real underwater SPAD data is very small. Moreover, the algorithm based on deep learning and simulated data for the removal of backward-scattering interference in underwater SPAD images demonstrates effectiveness in terms of both metrics and human observation. The model yields improvements in metrics such as the PSNR, SSIM, and entropy of 5.59 dB, 9.03%, and 0.84, respectively, demonstrating its superior performance.

Comparison of Proton and Gamma Irradiation on Single-Photon Avalanche Diodes

In this paper, the effects of proton and gamma irradiation on reach-through single-photon avalanche diodes (SPADs) are investigated. The I–V characteristics, gain and spectral response of SPAD devices under proton and gamma irradiation were measured at different proton energies and irradiation bias conditions. Comparison experiments of proton and gamma irradiation were performed in the radiation environment of geosynchronous transfer orbit (GTO) with two different radiation shielding designs at the same total ionizing dose (TID). The results show that after 30 MeV and 60 MeV proton irradiation, the leakage current and gain increase, while the spectral response decreases slightly. The leakage current degradation is more severe under the “ON”-bias condition compared to the “OFF”-bias condition, and it is more sensitive to the displacement radiation damage caused by protons compared to gamma rays under the same TID. Further analysis reveals that the non-elastic and elastic cross-section of protons in silicon is 1.05 × 105 times greater than that of gamma rays. This results in SPAD devices being more sensitive to displacement radiation damage than ionizing radiation damage. Under the designed shielding conditions, the leakage current, gain and spectral response parameters of SPADs do not show significant performance degradation in the orbit.

A simple Monte Carlo model for performance optimization of single photon avalanche diode

Single photon avalanche diode (SPAD) has the advantage of high internal gain, which is widely used in fluorescence detection and quantum communication. The high internal gain of the device is mainly due to avalanche multiplier effect. Therefore, it is of great significance to study avalanche multiplication effect for the design and performance optimization of SPAD devices. In this paper, a Simple Monte Carlo (SMC) model is implemented based on MATLAB, which includes interval phonon scattering and impact ionization of carriers. In this model, the electric field at different reverse bias voltages is extracted based on Technology-Computer- Aided- Design (TCAD). The model simulates the energy, velocity and impact ionization of carriers in the depletion region. The model has been verified on SPAD devices fabricated by 0.18um Bipolar - Complementary Metal Oxide Semiconductor - Diffused Metal Oxide Semiconductor (BCD) process. The SMC model simulates the dependence of the avalanche multiplication gain and excess noise factor of the SPAD device on the reverse bias voltage. In addition, the SMC model estimates the current–voltage (IV) characteristics and avalanche breakdown voltage of the device. In conclusion, the SMC model can provide guidance for the design and performance optimization of SPAD devices.

Modeling With RTS Noise Characterization of Novel Embedded Photogate Single-Photon Avalanche Diode for Circuit Simulations

Single-photon avalanche diodes (SPADs) are widely used for weak light detection due to their high gain and high sensitivity. Unfortunately, SPAD devices have random telegraph signal (RTS) noise during the avalanche transition phase, which makes circuit design more difficult. Therefore, the modeling of RTS noise in SPAD devices is of great significance for the design of signal processing circuits. However, RTS noise is not included in the traditional equivalent circuit model. In response to the above problems, this paper implements an equivalent circuit model with RTS noise based on the Cadence. The model is built based on the basic components in the library, and it has strong application universality. The model is validated in a novel embedded photogate SPAD device (EP-SPAD). It accurately simulates the RTS noise and IV characteristics of the EP-SPAD device. In addition, the threshold voltage of EP-SPAD device operating in Geiger mode is precisely defined based on the characteristics of RTS noise. When the reverse bias voltage is increased from 0 V to 15 V, the IV characteristics of the model are consistent with the EP-SPAD device.

Time-coordinated SPAD-based receiver for high-speed optical wireless communication

In an optical wireless communication system (OWC), the single photon avalanche diode (SPAD) can effectively improve the sensitivity of the receiver. However, the inter-slot interference (ISI) distortion and counting losses are inevitable because of the deadtime of the SPAD device. This effect is especially serious when the symbol time is similar than the deadtime. In this work, we propose a time-coordinated SPAD-based receiver scheme that enables multiple time-gated SPADs to reduce ISI distortion and counting losses in the high-speed transmission. The photon counting models and bit error rate (BER) model are established under the effect of ISI to the time-coordinated scheme. The results show that the proposed time-coordinated scheme not only can effectively reduce the ISI distortion and counting losses, but also can significantly improve the signal to noise ratio (SNR) of the receiver. In addition, compared with the free-running SPADs receiver under the same size, the background light tolerance and BER performance of the proposed time-coordinated receiver are better at the high signal power.

Design and Fabrication of Near Ultraviolet Enhanced Composite Single Photon Avalanche Diode for Fluorescence Lifetime Imaging

The near ultraviolet photon detection probability (PDP) of single photon avalanche diodes (SPADs) is very important for the fluorescence lifetime imaging. However, the PDP of traditional SPAD (T-SPAD) devices in the near-ultraviolet is not ideal, which is difficult to meet the requirements of fluorescence lifetime imaging. In response to the above problems, this paper realizes a near ultraviolet enhanced composite SPAD (NUEC-SPAD) based on photogate. The device is based on a photogate and a PN junction formed by P+/N-Well to detect photons. Therefore, the PDP of the device in the near ultraviolet is greatly improved. In addition, the shallow trench isolation (STI) and multiplication regions are isolated by photogate, and the dark count rate (DCR) of the device is greatly reduced. The principle of NUEC-SPAD device is simulated and verified based on the Technology-Computer-Aided-Design (TCAD). The NUEC-SPAD device and the T-SPAD device are fabricated based on the 0.18 μm BCD process. The experimental data show that the avalanche breakdown voltage of NUEC-SPAD device is 12 V. The device has good PDP in the range of 360 nm to 700 nm. Under the excess bias voltage of 0.5 V, the PDP of NUEC-SPAD device is 43.81% (@460 nm), which is 45.50% higher than that of T-SPAD device. Under the excess bias voltage of 1 V, the DCR of NUEC-SPAD device is only 0.24 Hz/μm2.

A Scaling Law for SPAD Pixel Miniaturization.

The growing demands on compact and high-definition single-photon avalanche diode (SPAD) arrays have motivated researchers to explore pixel miniaturization techniques to achieve sub-10 μm pixels. The scaling of the SPAD pixel size has an impact on key performance metrics, and it is, thereby, critical to conduct a systematic analysis of the underlying tradeoffs in miniaturized SPADs. On the basis of the general assumptions and constraints for layout geometry, we performed an analytical formulation of the scaling laws for the key metrics, such as the fill factor (FF), photon detection probability (PDP), dark count rate (DCR), correlated noise, and power consumption. Numerical calculations for various parameter sets indicated that some of the metrics, such as the DCR and power consumption, were improved by pixel miniaturization, whereas other metrics, such as the FF and PDP, were degraded. Comparison of the theoretically estimated scaling trends with previously published experimental results suggests that the scaling law analysis is in good agreement with practical SPAD devices. Our scaling law analysis could provide a useful tool to conduct a detailed performance comparison between various process, device, and layout configurations, which is essential for pushing the limit of SPAD pixel miniaturization toward sub-2 μm-pitch SPADs.

Design, Fabrication, and Verification of Blue-Extended Single-Photon Avalanche Diode with Low Dark Count Rate and High Photon Detection Efficiency

Single-photon avalanche diodes (SPADs) can detect extremely weak optical signals and are mostly used in single-photon imaging, quantum communication, medical detection, and other fields. In this paper, a low dark count rate (DCR) single-photon avalanche diode device is designed based on the 180 nm standard BCD process. The device has a good response in the 450~750 nm spectral range. The active area of the device adopts a P+/N-Well structure with a diameter of 20 µm. The low-doped N-Well increases the thickness of the depletion region and can effectively improve the detection sensitivity; the P-Well acts as a guard ring to prevent premature breakdown of the PN junction edge; the isolation effect of the deep N-Well reduces the noise coupling of the substrate. Use the TCAD simulation tool to verify the SPAD’s basic principles. The experimental test results show that the avalanche breakdown voltage of the device is 11.7 V. The dark count rate is only 123 Hz when the over-bias voltage is 1 V, and the peak photon detection efficiency (PDE) reaches 37.5% at the wavelength of 500 nm under the 0.5 V over-bias voltage. PDE exceeds 30% in the range of 460~640 nm spectral range, which has a good response in the blue band. The SPAD device provides certain design ideas for the research of fluorescence detectors.

Direct integration of micro-LEDs and a SPAD detector on a silicon CMOS chip for data communications and time-of-flight ranging.

We present integration of singulated micron-sized light emitting diodes (micro-LEDs) directly onto a silicon CMOS drive chip using a transfer printing method. An 8x8 micro-LED device array with individual control over each pixel is demonstrated with modulation bandwidths up to 50 MHz, limited by the large modulation depth of the driver chip. The 2 kHz frame rate CMOS driver also incorporates a Single Photon Avalanche Diode device thus allowing detection and transmission functionality on a single integrated chip. Visible light communications at data rates up to 1 Mbps, and time-of-flight ranging with cm-scale resolution are demonstrated using this hybrid integrated system.

Design and Measurement of Ring-Gate Single Photon Avalanche Diode with Low Dark Count Rate

Single photon avalanche diodes (SPAD) based on avalanche effect have been widely used in the detection of extremely weak light signals. Conventional SPAD devices manufactured with silicon-based CMOS technology have a high dark count rate (DCR), making it difficult to accurately detect single photon signals. This paper proposes a low dark count rate ring-gate SPAD (RG-SPAD) to solve above problems, and compares RG-SPAD with conventional SPAD (C-SPAD) and conventional dummy-gate SPAD (CDG-SPAD). Slivaco-Technology Computer Aided Design (TCAD) performs two-dimensional simulation of the device to verify the basic principles of SPAD. Three types of SPAD device are manufactured by standard BCD process. The passive quenching circuit is built to obtain the DCR of SPAD devices. The avalanche breakdown voltages of C-SPAD, CDG-SPAD and RG-SPAD are 11.55 V, 11.85 V and 11.4 V respectively. In order to test the dark count rate of SPAD devices, an over-bias voltage of 1 V was applied to three types of SPAD device under the same size condition (temperature: 22 °C). The DCR of RG-SPAD (186 Hz) with ring-gate structure is significantly lower than CDG-SPAD (378 Hz) with conventional dummy-gate structure and C-SPAD (498 Hz) with conventional structure. When the room temperature dropped to 18 °C, RG-SPAD still maintained the lowest DCR (148 Hz) among three types of device structure.

Reducing dark count of single-photon avalanche diode detector with polysilicon field plate

To suppress the effect of dark count noise on single photon avalanche diode (SPAD) detector, the mechanism and method of reducing the dark count rate (DCR) of SPAD device by using a polysilicon field plate is studied in this paper. Based on the 0.18-μm standard CMOS process, a polysilicon field plate located between the P+ active region and shallow trench isolation (STI) is deposited to reduce the dark count noise for a scaleable P+/P-well/deep N-well SPAD structure. Test results show that the DCR of SPAD device decreases by an order of magnitude after the deposition of polysilicon field plates, and its dark count performance at high temperature is even better than that of device without polysilicon field plate at room temperature. The TCAD simulation further indicates that the peak electric field in the guard ring region of the SPAD device is introduced into the STI by the field plate, and the overall electric field in the guard ring region is reduced by 25%. Finally, through modeling and calculating the DCR, the polysilicon field plate weakens the electric field of the guard ring region with high trap density, hence the trap-related DCR is significantly reduced. Therefore, the dark count performance of SPAD detector is effectively improved.

SPAD-Based Quantum Random Number Generator With an $N^{\rm{th}}$ -Order Rank Algorithm on FPGA

We present a compact, all-solid-state, low-cost quantum random number generator (QRNG) based on a single-photon avalanche diode (SPAD) and a field programmable gate array (FPGA). A new algorithm for random bit generation is described, ranking the inter-arrival times of a group of $M$ photons detected by the SPAD device, and processed directly on the FPGA. The proposed approach improves the efficiency of generated random bits per detected photon, spanning from 0.5 bits/photon in case of 0 order rank, up to 0.875 bits/photon for second order rank. By extending the algorithm to higher orders, the proposed system approaches the maximum theoretical value of 1.0 bit/photon. The rate of generation of random numbers is limited by the SPAD minimum deadtime, achieving an experimentally proven bit rate of 7.3 Mbps. The standard randomness statistical tests are passed for a wide range of photon fluxes and for all the implemented rank orders with no additional post-processing on the generated sequence.

A Simple Analytic Modeling Method for SPAD Timing Jitter Prediction

Timing jitter as a key performance of single-photon avalanche diode (SPAD) detectors plays a significant role in determining the fast temporal response behavior of the SPAD device. Nevertheless, few analytic models are developed to directly calculate the characteristic of timing jitter for its modeling difficulty. In this paper, we propose a simple analytic modeling method, which can predict the temporal response of SPADs, without using time-consuming Monte Carlo simulation. Model investigation incorporates avalanche current, avalanche buildup time, and jitter tail under different conditions. Furthermore, the key model parameters provided by Geiger mode technology computer-aided design simulation allow an accurate prediction on timing jitter. Analytical results indicate that for an SPAD device structure with a shallow P+/N-well junction in a 0.18- $\mu \text{m}$ CMOS technology, the Gaussian peak response with about 110-ps full-width at half-maximum and the exponential jitter tail are in good agreement with the measured data, validating the accuracy, and feasibility of this modeling method.

Experimental study on SPAD-based VLC systems after low-pass filtering

Abstract The practical output waveforms of single photon avalanche diode (SPAD) devices are some photon-counting pulse sequences during one symbol interval. The adaptive system and the well-known channel information are needed for the practical SPAD-based visible light communication (VLC) system. In this paper, we first study the performance of practical SPAD device after a low-pass filter. After low-pass filtering (LPF), the output of SPAD receiver transforms to be the continuous waveforms which is same as the traditional photodiode (PD)-based receiver. Then we put forward the fast blind union detection (FBUD) theory for the SPAD-based VLC system after LPF. In addition, we design a weak light communication experimental system with a red light-emitting diode (LED) status indicator and a practical SPAD device. After passing a 3 m free space transmission distance, the experimental results indicate that the performance of the proposed scheme is better than the well-established Poisson communication method and is worse than the practical output model under the dead time limit.

High-voltage integrated active quenching circuit for single photon count rate up to 80 Mcounts/s

Single photon avalanche diodes (SPADs) have been subject to a fast improvement in recent years. In particular, custom technologies specifically developed to fabricate SPAD devices give the designer the freedom to pursue the best detector performance required by applications. A significant breakthrough in this field is represented by the recent introduction of a red enhanced SPAD (RE-SPAD) technology, capable of attaining a good photon detection efficiency in the near infrared range (e.g. 40% at a wavelength of 800 nm) while maintaining a remarkable timing resolution of about 100ps full width at half maximum. Being planar, the RE-SPAD custom technology opened the way to the development of SPAD arrays particularly suited for demanding applications in the field of life sciences. However, to achieve such excellent performance custom SPAD detectors must be operated with an external active quenching circuit (AQC) designed on purpose. Next steps toward the development of compact and practical multichannel systems will require a new generation of monolithically integrated AQC arrays. In this paper we present a new, fully integrated AQC fabricated in a high-voltage 0.18 µm CMOS technology able to provide quenching pulses up to 50 Volts with fast leading and trailing edges. Although specifically designed for optimal operation of RE-SPAD devices, the new AQC is quite versatile: it can be used with any SPAD detector, regardless its fabrication technology, reaching remarkable count rates up to 80 Mcounts/s and generating a photon detection pulse with a timing jitter as low as 119 ps full width at half maximum. The compact design of our circuit has been specifically laid out to make this IC a suitable building block for monolithically integrated AQC arrays.

A Comprehensive and Accurate Analytical SPAD Model for Circuit Simulation

The single-photon avalanche diode (SPAD) is an attractive photosensor due to its high sensitivity and low dead time. In this paper, a comprehensive, accurate analytical SPAD circuit simulation model is proposed and implemented in Verilog-A hardware description language. It shows great application universality and is fully compatible with mainstream commercial circuit simulators. This model incorporates all important operating features of the SPAD. Most importantly, to the best of our knowledge, it is the first time that the band-to-band tunneling mechanism and the temporal dependence of after-pulsing probability are included in an SPAD circuit simulation model. The parameter extraction processes from interavalanche time measurement of a free-running SPAD device are discussed. The simulation results indicate that the proposed model works well. In addition, the primary dark counts from the model are validated against the measurement results. A maximum relative error of 8.7% is observed at 20 °C with an excess voltage of 0.5 V. The accuracy of this paper can be greatly improved by using more accurate physical parameters available from the SPAD fabrication vendor.

A SPAD-Based QVGA Image Sensor for Single-Photon Counting and Quanta Imaging

A CMOS single-photon avalanche diode (SPAD)-based quarter video graphics array image sensor with 8- $\mu \text{m}$ pixel pitch and 26.8% fill factor (FF) is presented. The combination of analog pixel electronics and scalable shared-well SPAD devices facilitates high-resolution, high-FF SPAD imaging arrays exhibiting photon shot-noise-limited statistics. The SPAD has 47 counts/s dark count rate at 1.5 V excess bias (EB), 39.5% photon detection probability (PDP) at 480 nm, and a minimum of 1.1 ns dead time at 1 V EB. Analog single-photon counting imaging is demonstrated with maximum 14.2-mV/SPAD event sensitivity and 0.06e− minimum equivalent read noise. Binary quanta image sensor (QIS) 16-kframes/s real-time oversampling is shown, verifying single-photon QIS theory with $4.6\times $ overexposure latitude and 0.168e− read noise.

Radiation tests of single photon avalanche diode for space applications

Single photon avalanche diodes (SPADs) have been recently studied as photodetectors for applications in space missions. In this presentation we report the results of radiation hardness test on large area SPAD (actual results refer to SPADs having 500μm diameter). Dark counts rate as low as few kHz at −10°C has been obtained for the 500μm devices, before irradiation. We performed bulk damage and total dose radiation tests with protons and gamma-rays in order to evaluate their radiation hardness properties and their suitability for application in a Low Earth Orbit (LEO) space mission. With this aim SPAD devices have been irradiated using up to 20krad total dose with gamma-rays and 5krad with protons. The test performed show that large area SPADs are very sensitive to proton doses as low as 2×108 (1MeVeq)n/cm2 with a significant increase in dark counts rate (DCR) as well as in the manifestation of the “random telegraph signal” effect. Annealing studies at room temperature (RT) and at 80°C have been carried out, showing a high decrease of DCR after 24–48h at RT. Lower protons doses in the range 1–10×107 (1MeVeq)n/cm2 result in a lower increase of DCR suggesting that the large-area SPADs tested in this study are well suitable for application in low-inclination LEO, particularly useful for gamma-ray astrophysics.

Avalanche Current Measurements in SPADs by Means of Hot-Carrier Luminescence

A growing number of applications require arrays of single-photon avalanche diode (SPAD) detectors with low timing jitter. In order to improve jitter without compromising other performance parameters, a clear understanding of avalanche dynamics and statistics is necessary. In this work, a noninvasive electro-luminescence technique has been employed to investigate the current growing in a SPAD device. The obtained results let us assess, for the first time experimentally, the avalanche spreading speeds and also confirmed our assumption that the current growth pace and its statistics critically depend on the space charge effects.