LiDAR has become a critical requirement for Advanved Driver Assistance Systems (ADAS) as the automotive industry moves towards improved driver safety and autonomous cars. Silicon Photomultipliers (SiPM) and Single Photon Avalanche Diodes (SPAD) sensors are emerging as the most promising sensor technology for long range, >100m, direct time-of-flight LiDAR that needs to function in bright daylight and with low reflectance targets.
SensL is developing a new range of SiPM, the R-Series, that have improved detection efficiency at longer wavelengths used in LiDAR. In parallel to the sensor development, SensL is working to understand the fundamental advantages SiPM and SPAD sensor arrays provide long-range, ADAS LiDAR systems.
It will be shown that to achieve long range LiDAR with eye-safe lasers, a sensor with single photon sensitivity is required. This is due to the low number of returned photons from distances greater than 100m. When ambient daylight conditions are taken into account, the small returned signal at these distances can be easily lost in the noise and histogramming multiple laser pulses will be shown to provide the only method which allows for accurate time of flight ranging operation.
The histogramming technique and the architecture used to implement it will be described. A portable long-range LiDAR demonstrator using SiPM sensors has been developed and will be presented including range accuracy versus distance and low reflective targets. This will be compared to a detailed Monte Carlo model which will be shown to accurately describes SiPM and SPAD array operation in LiDAR ranging.
The “sonic region” of the Sun corona remains extremely difficult to observe with spatial resolution and sensitivity sufficient to understand the fine scale phenomena that govern the quiescent solar corona, as well as phenomena that lead to coronal mass ejections (CMEs), which influence space weather. Improvement on this front requires eclipse-like conditions over long observation times. The space-borne coronagraphs flown so far provided a continuous coverage of the external parts of the corona but their over-occulting system did not permit to analyse the part of the white-light corona where the main coronal mass is concentrated. The proposed PROBA-3 Coronagraph System, also known as ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun), with its novel design, will be the first space coronagraph to cover the range of radial distances between ~1.08 and 3 solar radii where the magnetic field plays a crucial role in the coronal dynamics, thus providing continuous observational conditions very close to those during a total solar eclipse. PROBA-3 is first a mission devoted to the in-orbit demonstration of precise formation flying techniques and technologies for future European missions, which will fly ASPIICS as primary payload. The instrument is distributed over two satellites flying in formation (approx. 150m apart) to form a giant coronagraph capable of producing a nearly perfect eclipse allowing observing the sun corona closer to the rim than ever before. The coronagraph instrument is developed by a large European consortium including about 20 partners from 7 countries under the auspices of the European Space Agency. This paper is reviewing the recent improvements and design updates of the ASPIICS instrument as it is stepping into the detailed design phase.
Packaging can have a significant impact on the performance characteristics of Silicon Photomultipliers (SiPM) sensors as well as having an impact on reliability and yield. To provide the highest performance possible, SensL have recently developed and tested a surface mount, through silicon via (TSV) package that provides high array fill factor, high photon detection efficiency (PDE) and magnetic resonance imaging (MRI) system compatibility. The PDE of TSV packaged sensors will be shown to be the highest when compared to traditional SiPM package types. In addition the PDE in the UV and blue region will be shown to approach that of unprotected bare die. Additionally, the TSV package has minimal deadspace outside of the active area which will be shown to allow close packing when used in a sensor array. It will be shown that arrays of TSV sensors have the highest fill factor currently possible when creating arrays from singulated die. Additionally, it will be shown that TSV parts are non-magnetic and results of images taken with the TSV SiPM in a 3 Tesla magnetic resonance imaging (MRI) system will be shown to have no impact on the MRI system.
SensL C-Series Silicon Photomultiplier (SiPM) sensors are fabricated in a high-volume CMOS foundry to a custom SensL process, and packaged as a reflow solderable surface mount device. Advances in SiPM production have resulted in significant improvement in PDE, dark current as well as tighter breakdown voltage uniformity for the C-Series SiPM sensors. The SiPM are fabricated with a shallow P-on-N junction optimized for the detection of shorter wavelength photons, with a peak PDE of 41% at 420nm and excellent sensitivity extending to wavelengths <300nm. The dark currents have been reduced through the reduction of damage during semiconductor processing and an order of magnitude reduction has been achieved. The breakdown voltage variation has been improved through process optimization to minimize variations. With these process improvements typical dark count rates of ~30kHz/mm2 are achieved simultaneously with breakdown voltage uniformity of ±213mV demonstrated. In addition, application specific measurements of CRT (Coincidence Resolving Time) that are relevant to PET (positron emission tomography) will be shown to be 210ps at 7.5V overvoltage. In addition to device characterization work, this paper will address the wafer-level fabrication and testing, package level testing required by high volume SiPM sensor applications.
This publication details CMOS foundry fabrication, reliability stress assessment, and packaged sensor test results obtained during qualification of the SensL B-Series silicon photomultiplier (SiPM). SiPM sensors with active-area dimensions of 1, 3, and 6 mm were fabricated and tested to provide a comprehensive review of SiPM performance highlighted by fast output rise times of 300 ps and photon detection efficiency of greater than 41%, combined with low afterpulsing and crosstalk. Measurements important for medical imaging positron emission tomography systems that rely on time-of-flight detectors were completed. Results with LSYO:Ce scintillation crystals of 3×3×20 mm3 demonstrated a 225±2-ps coincidence resolving time (CRT), and the fast output is shown to allow for simultaneous acquisition of CRT and energy resolution. The wafer level test results from ∼150 k 3-mm SiPM are shown to demonstrate a mean breakdown voltage value of 24.69 V with a standard deviation of 0.073 V. The SiPM output optical uniformity is shown to be ±10% at a single supply voltage of 29.5 V. Finally, reliability stress assessment to Joint Electron Device Engineering Council (JEDEC) industry standards is detailed and shown to have been completed with all SiPM passing. This is the first qualification and reliability stress assessment program run to industry standards that has been reported on SiPM.
PROBA-3 is a mission devoted to the in-orbit demonstration of precise formation flying techniques and technologies for future ESA missions. PROBA-3 will fly ASPIICS (Association de Satellites pour l’Imagerie et l’Interferométrie de la Couronne Solaire) as primary payload, which makes use of the formation flying technique to form a giant coronagraph capable of producing a nearly perfect eclipse allowing to observe the sun corona closer to the rim than ever before. The coronagraph is distributed over two satellites flying in formation (approx. 150m apart). The so called Coronagraph Satellite carries the camera and the so called Occulter Satellite carries the sun occulter disc. This paper is reviewing the design and evolution of the ASPIICS instrument as at the beginning of Phase C/D.
Avalanche photodiodes are very well suited and extensively used for low light application. In this paper we present a devise using avalanche photodiodes in conjunction with a pulsed laser-source to be used as an optical altimeter. The extreme sensitivity of a dedicated silicon SPAD array is combined with a versatile standard CMOS readout circuit to achieve unique performances. This imaging device is able to perform ranging with four centimeters accuracy over five kilometers distance. It is also capable of delivering quantum limited images. Development of the readout circuit will be disclosed as well as measurement results performed on the final device.
3D LIDAR imaging is a key enabling technology for automatic navigation of future spacecraft, including landing,
rendezvous and docking and rover navigation. Landing is typically the most demanding task because of the range of
operation, speed of movement, field of view (FOV) and the spatial resolution required. When these parameters are
combined with limited mass and power budget, required for interplanetary operations, the technological challenge
becomes significant and innovative solutions must be found. Single Photon Avalanche Photodiodes (SPADs) can reduce
the laser power by orders of magnitude, array detector format can speed up the data acquisition while some limited
scanning may extend the FOV without pressure on the mechanics. In the same time, SPADs have long dead times that
complicate their use for rangefinding. Optimization and balance between the instrument subsystems are required. We
discuss how the implementation of real-time control as an integral part of the LIDAR allows the use of SPAD array
detectors in conditions of high dynamics. The result is a projected performance of more than 1 million 3D pixels/s at a
distance of several kilometers within a small mass/power package. The work is related to ESA technology development
for future planetary landing missions.
Large area optical detection systems are required for applications including cell imaging, spectroscopy, nuclear
medicine, bio diagnostics, radiation detection and high energy physics. Each of these applications requires that a detector
or detector arrays be closely coupled with light sources or optical couplers such as fibres or light couplers. In this paper,
the scaling of novel Silicon Photomultiplier detectors to tile across a large area is presented. In particular, a novel method
is discussed for compact packaging of SPM detectors into a tiled 2D detector array for large area imaging and 2D spatial
detection. The SPM detector has performance characteristics comparable to vacuum photon multiplier tubes used in
these applications today but offers several performance and system design advantages including spatial resolution,
optical over exposure, small form factor, weight, magnetic insensitivity and low bias operation.
Current state of the art high resolution counting modules, specifically designed for high timing resolution applications,
are largely based on a computer card format. This has tended to result in a costly solution that is restricted to the
computer it resides in. We describe a four channel timing module that interfaces to a computer via a USB port and
operates with a resolution of less than 100 picoseconds. The core design of the system is an advanced field
programmable gate array (FPGA) interfacing to a precision time interval measurement module, mass memory block and
a high speed USB 2.0 serial data port. The FPGA design allows the module to operate in a number of modes allowing
both continuous recording of photon events (time-tagging) and repetitive time binning. In time-tag mode the system
reports, for each photon event, the high resolution time along with the chronological time (macro time) and the channel
ID. The time-tags are uploaded in real time to a host computer via a high speed USB port allowing continuous storage
to computer memory of up to 4 millions photons per second. In time-bin mode, binning is carried out with count rates
up to 10 million photons per second. Each curve resides in a block of 128,000 time-bins each with a resolution
programmable down to less than 100 picoseconds. Each bin has a limit of 65535 hits allowing autonomous curve
recording until a bin reaches the maximum count or the system is commanded to halt. Due to the large memory storage,
several curves/experiments can be stored in the system prior to uploading to the host computer for analysis. This makes
this module ideal for integration into high timing resolution specific applications such as laser ranging and fluorescence
lifetime imaging using techniques such as time correlated single photon counting (TCSPC).
This paper describes the integration of an automatic gain and bias control circuit for avalanche photodiodes with the Sensl PCMPLusX photon counting module. The combination is a self contained module with integrated sensor, power supply, cooling and full microprocessor control system. The sensors can be configured remotely via a PC enabling the user to optimize the sensor performance for a particular application. The system has four channels which can be configured either in photon counting mode or gain control mode. With the photon counting module enabled the user can optimize detector characteristics such as quantum efficiency, dark count, amplification and operating temperature for specific applications. With the gain control module enabled the system allows the user to program the sensor to a desired multiplication gain factor and the circuit to automatically adjust for fluctuations in supply voltage.
This paper demonstrates the experimental results of combining new state-of-the-art Geiger mode avalanche photodiodes with an integrated hybrid active/passive quenching circuit. This creates an ultra-compact form factor for a low-light level detection module. Both devices, the photodiode and the quenching circuit, are fabricated using conventional CMOS process technology and wafer substrates. The photodiodes operate at low voltage levels (30 V to 40V). Detector active areas are of various dimensions (10μm to 50μm) and shapes (circular, cylindrical or square). The integrated active/passive quenching circuit is included on a 2.5 mm × 2.5 mm die, which has the functionalities of bias conditioning, passive/active quench, output signal generation and active recharge. The prototypes are hybrid packaged onto a PCB substrate. The module is characterised for detecting very low level optical signals such as the single photon activities. Parameters such as dark counts, timing jitter, and responsivity will be shown for the compact detection module. Our findings show that the proposed avalanche photodiode operation is considerably faster than the conventional discrete systems and the module size is greatly reduced.
There is a need for low cost, miniature, integrated optical systems for bioassay monitoring to meet the growing in vitro and point-of-care diagnostics markets. To this end, we are investigating the use of silicon photomultipliers (SiPM) as device upon which to base our technology development. SiPMs have been used successfully in many high-energy physics applications, but their application as a fully integrated biological detection platform has not been shown. In this paper we will present a new detection platform for the measurement of fluorescent biomolecules at much lower concentrations than commercially available systems. Our results show approaches that demonstrate the use of SiPM for the detection of fluorescent proteins and fluorescent-labelled DNA sequences. The SiPM and sample platforms are integrated so that the minimum distance separating the detector from the sample is realised. In addition, direct immobilisation of the DNA sequences onto the SiPM surface is achieved. This combined approach shows improved sensitivities for both the fluorescent proteins and fluorescent-labelled DNA.
We are presenting results that show the use of SiPM as a successful technology for the measurement of fluorescent biomolecules at improved lower concentrations.
For future fully integrated sensing applications, a CMOS sensor will be required. New CMOS photon counting sensors have recently become available and these devices provide high quantum efficiency, photon counting sensitivity, low power and new devices in arrays and with on-chip electronics. In biological applications, photon counting is focused on the detection of low intensity fluorescence signals from fluorophores conjugated to proteins or nucleic acid biomarkers
from fluorescent proteins. We describe the development of a novel microtitre plate reader format, or bioassay platform that incorporates arrays of photon counting detectors for multiple parallel readout and data acquisition. Using Pyrex wafers, we have designed and fabricated custom-made reaction wells using Pyrex and deep ion trench etched silicon, which produce optically clear structures to facilitate fluorescence detection in biological samples volumes of 2 nL to 2 μL. For initial verification of the system, a new photon counting detector from SensL is used to determine the effectiveness of the wells as the bioassay platform. The compact unit consists of a fibre coupled silicon photon counting sensor, thermoelectric cooler, thermoelectric controller, active quenching circuit, power supplies, and an USB interface to the operating software. Included in the module is a counter with time binning capability. Sensitivity increases of more than two orders of magnitude in fluorescence detection are expected over commercially available instruments. This system demonstrates that a miniaturized, low cost solution is possible for fluorescence bioassay detection, which can be used to meet growing demands in the in vitro diagnostics and Point of Care markets.
The many advantages of silicon such as low cost, abundancy and a level of maturity that allows for very large scale integration, means that silicon is the most commonly used semiconductor in microelectronics and optoelectronic devices. Silicon, however, has one disadvantage, this being that it is unable to absorb light greater than 1100 nm. The two primary telecommunications wavelengths, 1300 nm and 1550 nm, can therefore not be detected. An interesting method used to extend silicon's wavelength range is the formation of black silicon on the silicon surface. Black silicon is formed when gases that are passed over the silicon react and etch the silicon surface, forming a dark spiky pattern. When light is shone on such a pattern, it repeatedly bounces back and forth between the spikes thus reducing surface reflection and trapping the light. This reduced reflectance and light trapping increases the sensitivity of the silicon to long wavelengths and makes it viable for use in a wide range of commercial devices such as infrared detectors and solar cells. This paper presents novel black silicon PIN photodiodes of various sizes (25 mm2, 4 mm2 and 1 mm2). The diodes have been extensively characterized at wafer level, with breakdown voltage, dark current, shunt resistance, threshold voltage and junction capacitance measurements being made. Extensive responsivity measurements were also performed and it was established that the black silicon surface resulted in responsivity increases of greater
than 50 % at long wavelengths (≈ 1100 nm).
Previous generation low light detection platforms have been based on the photomultiplier tube (PMT) or the silicon single photon counting module (SPCM) from Perkin Elmer1. A new generation of silicon CMOS compatible photon counting sensors are being developed offering high quantum efficiency, low operating voltage, high levels of robustness and compatibility with CMOS processing for integration into large format imaging arrays. This latest generation yields a new detector for emerging applications which demand photon counting performance providing high performance and flexibility not possible to date. We describe a 4-channel photon detection platform, which allows the use of 4 separate photon counting detectors in either free space or fibre-coupled mode. The platform is scalable up to 16 channels with plug in modules allowing active quenching or Peltier cooling as required. A graphical user interface allows feedback and control of all device parameters. We show a novel ability to integrate separate detection modules to extend the dynamic range of the system. This allows a PIN or APD mode detector to be used alongside sensitive photon counting detectors. An advanced FPGA and microcontroller interface has been designed which allows simultaneous time binning of counting rates and readout of the analog signals when used with linear detectors. This new architecture will be discussed, presenting a full characterization of count rate, quantum efficiency, time binning and sensitivity across the broad spectrum of light flux applicable to PIN diodes, APDs and Geiger-mode photon counting sensors.
The operation and performance of multi-pixel, Geiger-mode APD structures referred to as Silicon Photomultiplier (SPM) are reported. The SPM is a solid state device that has emerged over the last decade as a promising alternative to vacuum PMTs. This is due to their comparable performance in addition to their lower bias operation and power consumption, insensitivity to magnetic fields and ambient light, smaller size and ruggedness. Applications for these detectors are numerous and include life sciences, nuclear medicine, particle physics, microscopy and general instrumentation. With SPM devices, many geometrical and device parameters can be adjusted to optimize their performance for a particular application. In this paper, Monte Carlo simulations and experimental results for 1mm2 SPM structures are reported. In addition, trade-offs involved in optimizing the SPM in terms of the number and size of pixels for a given light intensity, and its affect on the dynamic range are discussed.
In the field of fluorescent microscopy, neuronal activity, diabetes and drug treatment are a few of the wide ranging biomedical applications that can be monitored with the use of dye markers. Historically, in-vivo fluorescent detectors consist of implantable probes coupled by optical fibre to sophisticated bench-top instrumentation. These systems typically use laser light to excite the fluorescent marker dies and using sensors, such as the photo-multiplier tube (PMT) or charge coupled devices (CCD), detect the fluorescent light that is filtered from the total excitation. Such systems are large and expensive. In this paper we highlight the first steps toward a fully implantable in-vivo fluorescence detection system. The aim is to make the detector system small, low cost and disposable. The current prototype is a hybrid platform consisting of a vertical cavity surface emitting laser (VCSEL) to provide the excitation and a filtered solid state Geiger mode avalanche photo-diode (APD) to detect the emitted fluorescence. Fluorescence detection requires measurement of extremely low levels of light so the proposed APD detectors combine the ability to count individual photons with the added advantage of being small in size. At present the exciter and sensor are mounted on a hybrid PCB inside a 3mm diameter glass tube.This is wired to external electronics, which provide quenching, photon counting and a PC interface. In this configuration, the set-up can be used for in-vitro experimentation and in-vivo analysis conducted on animals such as mice.
Geiger Mode avalanche photodiodes offer single photon detection, however, conventional biasing and processing circuitry make arrays impractical to implement. A novel photon counting concept is proposed which greatly simplifies the circuitry required for each device, giving the potential for large, single photon sensitive, imaging arrays. This is known as the DigitalAPD. The DigitalAPD treats each device as a capacitor. During a write, the capacitor is periodically charged to photon counting mode and then left open circuit. The arrival of photons causes the charge to be lost and this is later detected during a read phase. Arrays of these devices have been successfully fabricated and a read out architecture, employing well known memory addressing and scanning techniques to achieve fast frame rates with a minimum of circuitry, has been developed. A discrete prototype has been built to demonstrate the DigitalAPD with a 4x4 array. Line rates of up to 5MHz have been observed using discrete electronics. The frame burst can be transferred to a computer where the arrival of single photons at any of the 16 locations can be examined, frame by frame. The DigitalAPD concept is highly scalable and is soon to be extended to a fully integrated implementation for use with larger 32x32 and 100x100 APD arrays.
Recent advances in silicon based photon counting detectors have lead to the development of a new photon counting module. The detector for the module is fabricated in standard bulk silicon using complementary metal oxide semiconductor (CMOS) processing steps. High quantum efficiency across the visible spectrum combinedwith low timing
jitter (150ps) provide ideal characteristics for photon counting applications. Through careful selection of components and operating conditions, the time-walk, which degrades the timing resolution of silicon photon counting detectors is minimised. The detector module is designed with a microprocessor interface which allows the internal operating characteristics to be optimised depending on the application. This work seeks to provide a overview of current photon counting detectors demonstrate the tradeoffs associated with each detector and present the new detector module demonstrating operation with zero time-walk affect.
Novel integrated sensors will be required for future detection
platforms for the measurement of fluorescence and luminescence. The
current trend towards integration of optical detectors and the broad
advances in optical emitting dyes and proteins will be combined
in robust, low-cost, point-of-use, diagnostic equipment. To this end
we are experimenting with an integrated optical hybrid sensing device which will combine a flip-chipped, array of solid-state single photon counting detectors with surface mount passive quench circuits on a conventional glass substrate. This flip-chipped arrangement both 1) increases the speed of response of the detector and 2) increases the
robustness and ease of integration and reduces single photon detector handling requirements. The potential of integrated solid-state photon detectors will be demonstrated for the real-time quantitative detection of luciferase, a light emitting protein expression reporter molecule. A 15μm solid-state Geiger-mode avalanche photodiode (APD) operating in single photon counting mode will be compared with a standard photomultiplier tube (PMT) for luciferase luminescence
detection. Detection levels of 2×106 and 1×107 enzyme molecules will be demonstrated for PMT and Geiger-mode APD respectively. The size of the Geiger-mode APD active area will be shown to be the limiting factor in luciferase signal detection for non-integrated applications. A simple geometric model will show that detection limits of 1×104 are achievable in integrated sensing platforms using room temperature operated single photon counting detectors.
Large-area Geiger-mode avalanche photodiodes (GMAPs) that are designed to be compatible with a 1.5μm CMOS and silicon-on-insulator (SOI) CMOS process are presented here as candidate detectors for use in optoelectronic integrated circuits (OEICs). The photodetectors have 250μm and 500μm diameter active areas with 20um virtual guard ring overlaps. The GMAPs have a breakdown voltage of -30V and will be biased below breakdown in avalanche mode. The diodes' junction capacitances at 5V reverse bias are 11.66pF and 41.71pF respectively and 4.99pF and 17.95pF respectively at 27V reverse bias. The 250μm photodiode has a calculated bandwidth of 454MHz when biased at -5V while the 500μm diode has a calculated bandwidth of 142MHz when biased at -5V calculated using small-signal equivalent circuits for the devices.
New Geiger Mode Avalanche Photodiodes (GM-APD) have been designed and characterized specifically for use in microarray systems. Critical parameters such as excess reverse bias voltage, hold-off time and optimum operating temperature have been experimentally determined for these photon-counting devices. The photon detection probability, dark count rate and afterpulsing probability have been measured under different operating conditions. An active- quench circuit (AQC) is presented for operating these GM- APDs. This circuit is relatively simple, robust and has such benefits as reducing average power dissipation and afterpulsing. Arrays of these GM-APDs have already been designed and together with AQCs open up the possibility of having a solid-state microarray detector that enables parallel analysis on a single chip. Another advantage of these GM-APDs over current technology is their low voltage CMOS compatibility which could allow for the fabrication of an AQC on the same device. Small are detectors have already been employed in the time-resolved detection of fluorescence from labeled proteins. It is envisaged that operating these new GM-APDs with this active-quench circuit will have numerous applications for the detection of fluorescence in microarray systems.