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Pushing technologies: Single-Photon avalanche diode arrays

Authors:

Abstract

We present the development of silicon monolithic arrays of 60 photon-counters (SPADA, Single-Photon Avalanche Diode Array) for the visible. The SPADA system is suitable for state-of-the-art Adaptive Optics operations and Fast Transient image acquisitions, at quite a fraction of the current cost of imaging arrays. The fabricated solid-state photon counters are rugged, easy to be integrated in the optical system. They are free from readout noise and provide very fast frame-rates (>10kHz, for visible corrections) and nanosecond electronic gating (for ranging the up-going laser beam). The detection head has been integrated into an optomechanical system suitable for alignment and focusing in available astrophysics telescopes. The detection electronics includes an integrated Active Quenching Circuits for each pixel of the array. The real-time data-processing board is implemented into FPGA and DSP and is configurable for dealing with different applications: the extraction of the curvature wavefront for AO applications, and the acquisition and processing of two-dimensional images with fast frame rate. A remote host computer controls all the SPADA blocks and uploads the processed information and images. We report the optical and electrical characterization of the detectors and the associated electronics.
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-@<-6;176<7;9=):-,)::)A;7.807<76+7=6<-:;1;6)<=:)44A,-;1:)*4-.7:<0-=;-);;-6;7:;7.# )6,1;167=:84)6;
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,1/1<)41<1;.);<-:;1584-:)6,57:-:7*=;<<0)6;)6,1<+)6*-16,=;<:1)44A8:7,=+-,?1<047?-:+7;<1/;07?;
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807<7,17,-;16<-/:)<-,-4-+<:761+.7:,-<-+<16/<0-1/61<1767.-)+0-4-5-6<)*7):,.7:807<76+7=6<16/)6,:-)4<15-
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,-<-+<7:80A;1+;51+:7-4-+<:761+;-4-+<:761+16;<:=5-6<)<176)6,,)<)8:7+-;;16/6,--,.:75<0-,->1+-;<)6,8716<
/-75-<:1-;4)A7=<;)6,.)*:1+)<1768:7+-;;16/;<-8;7.-)+0" 5=;<*-,-;1/6-,)6,1584-5-6<-,*A<)316/16<7
)++7=6<<0-5)16:-9=1:-5-6<;7.01/0,-<-+<176-..1+1-6+A47?671;-)6,<7)>71,;8=:17=;+7=8416/;)576/<0-)::)A
SPIE USE, V. 2 5490-38 (p.2 of 11) / Color: No / Format: A4/ AF: A4 / Date: 2004-06-09 01:52:36
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SPIE USE, V. 2 5490-38 (p.3 of 11) / Color: No / Format: A4/ AF: A4 / Date: 2004-06-09 01:52:36
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SPIE USE, V. 2 5490-38 (p.4 of 11) / Color: No / Format: A4/ AF: A4 / Date: 2004-06-09 01:52:36
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SPIE USE, V. 2 5490-38 (p.5 of 11) / Color: No / Format: A4/ AF: A4 / Date: 2004-06-09 01:52:36
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SPIE USE, V. 2 5490-38 (p.10 of 11) / Color: No / Format: A4/ AF: A4 / Date: 2004-06-09 01:52:36
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SPIE USE, V. 2 5490-38 (p.11 of 11) / Color: No / Format: A4/ AF: A4 / Date: 2004-06-09 01:52:36
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... McIntyre and Webb introduced one of the first reach-through SPADs on silicon with a custom technology with ultra-low doped p-substrate silicon [15], [16]. The depletion layer of the device was 20 to 100 µm thick and the breakdown voltage was 100 to 500 volts. ...
... The SPAD active area was 50-500 µm and early edge breakdown effects were prevented by a p + enrichment and by reducing the silicon thickness over it by etching the wafer. [15]. ...
Article
Quantum parasitic effects and miniaturization of Single Photon Avalanche Diodes in deep-submicron technologies have been studied in this thesis in detail. Tunneling noise and Random Telegraph Signal (RTS) noise have been the main two parasitic effects addressed comprehensively. While the fundamental equations for tunneling count rate in SPADs have been presented, the tunneling study has been performed by comparing two different topologies of SPADs on the same technology. The tunneling evaluation has been performed by implementing a new n-tub guard ring SPAD in 0.35 μm standard CMOS technology. The NTGR SPAD has been characterized theoretically by simulations, and experiments. The tunneling noise effects have been verified in the I-V characteristics and Dark Count Rate responses of the new NTGR SPAD. While the NTGR SPAD has shown 3 % improvement in the maximum Photon Detection Probability (PDP), the timing jitter Full Width Half Maximum (FWHM) has been increased from 80 ps in p-tub guard ring SPAD to 152 ps in the NTGR SPAD. The breakdown voltage has been decreased 4.1 V due to using different doping profiles for NTGR SPAD implementation. Avalanche photoemission of the active area of NTGR SPAD demonstrated the ability for single photon detection in comparison with the other diodes, which show photoemssion in guard rings as a sign of Premature Edge Breakdown (PEB). The second parasitic effect which has been studied in this thesis was the RTS behavior of dark count rate (DCR); this is characterized as a bistability and multistability of DCR. RTS behavior of DCR has been observed in a SPAD fabricated in 0.8 μm CMOS technology and in four proton-irradiated SPADs designed and fabricated in 0.35 μm CMOS technology. To the best of our knowledge, this was the first time RTS behavior of DCR has been reported in SPADs in any CMOS technology. RTS characteristics have been evaluated experimentally and verified theoretically with respect to the bias and temperature. The RTS hypothesis of the fluctuations has been verified by measurements that have been in excellent agreement with the theory. The RTS behavior is expected to affect large array of SPAD detectors being used for D imaging applications. Demonstrating the functionality of SPADs in deep-submicron technologies has been the second main challenge of this thesis. We have demonstrated that singlephoton detectors can be fabricated in commercial deep-submicron CMOS processes. Miniaturization has been explored with the first SPAD designed and successfully tested in technologies smaller than 130nm. The proposed structures, implemented in 90nm standard CMOS technology, emerged from a systematic study aimed at miniaturization, while optimizing overall performance. The guard ring design has been the result of an extensive modeling effort aimed at constraining the multiplication region within a well-defined area where the electric field exceeds the critical value for impact ionization. By implementing different SPAD structures, we have studied the geometric trade-offs involved in the design of deep-submicron SPADs. Numerous SPADs with different arrangements of doping layers and different guard ring sizes have been implemented. Among them, as many as 45 structures were functional with a range of well-defined, reproducible breakdown voltages. The implemented structures have also been simulated and characterized. The detectors feature an octagonal multiplication region and a guard ring to prevent PEB using a standard mask set, exclusively. The proposed structure emerged from a systematic study aimed at miniaturization, while optimizing the overall performance. The devices exhibit a DCR of 8.1 kHz, a maximum PDP of 14 % at maximum excess bias. At 0.13 V of excess bias, a PDP of 9 % and a jitter of 398ps at a wavelength of 637 nm, were measured at room temperature. An afterpulsing probability of 32 % was measured at the nominal dead time. The main weak point of SPADs which have been demonstrated in this thesis in 90nm technology was the lack of isolation with the substrate, while different solutions have been proposed confining the NTGR SPAD, not to communicate with the substrate. Simulation based analysis of SPADs designed in 65nm CMOS technology has been described in the last section. The design of SPADs in 65nm technology was based on the characterization results of functional SPADs in 90nm technology. While implementation of SPADs in imaging CMOS technologies can lead to better performance due to the special layers, one of the main achievements of this thesis has been the demonstration of SPAD in a standard CMOS technology without employment of imaging doping layers. Because of the isolation issues described above, novel circuits have been implemented for the SPAD quenching and pulse detection.
... Silicon APDs can provide both the QE of silicon and the amplification (> 10 4 ) necessary to operate as a noiseless pixel. The development of APD arrays is just beginning using CMOS technology [14] but the QEs are not high and the filling factor is quite low. A thick silicon pn APD design that could be backside illuminated exists [15]. ...
Article
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We describe the development of an imaging photon counting detector based on microchannel plates (MCPs) with specialized readout integrated circuits (ROICs). The detector consists of a photocathode, MCPs that amplify the photoelectron, and a ROIC that has event counters on every pixel. In this detector, it is the event counts that are integrated, not the charge, and there is no associated readout noise. Also, the integrated signal per pixel is already digital and the frame can therefore be readout very fast without noise penalty. The quantum efficiency is dependent on the photocathode chosen and can be tailored to the application (e.g. FUV solar blind to the near infrared). Both the electronic counters and the MCPs can be gated to nanosecond accuracy for ranging applications. The first application for this detector concept is a 256x256 optical wavefront sensor using the Medipix2 ROIC funded by the NSF Adaptive Optics Development Program. This detector can achieve a frame rate of 1 kHz with zero readout noise and 37% QE at 600 nm. We have demonstrated the spatial resolution and event rate (~1 GHz) of this detector with a laboratory vacuum test detector in the UV and are in the process of integrating this detector into a vacuum tube with a GaAs photocathode. We will also present possible future ROICs to be used with MCP technology to achieve faster frame rates or more pixels or both and discuss the possibility of using avalanche photodiodes (APDs) as the input photoconverter/amplifier rather than MCPs to increase the optical QE.
... Quantum efficiencies for commonly used optical regime photocathodes (Sources: www.ittnv.com, www.hamamatsu.com), and the more recent GaAs advances11 . ...
Article
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Future wavefront sensors for AO on large telescopes will require a large number of pixels and must operate at high frame rates. Unfortunately for CCDs, there is a readout noise penalty for operating faster, and this noise can add up rather quickly when considering the number of pixels required for the extended shape of a sodium laser guide star observed with a large telescope. Imaging photon counting detectors have zero readout noise and many pixels, but have suffered in the past with low QE at the longer wavelengths (>500 nm). Recent developments in GaAs photocathode technology, CMOS ASIC readouts and FPGA processing electronics have resulted in noiseless WFS detector designs that are competitive with silicon array detectors, though at ~40% the QE of CCDs. We review noiseless array detectors and compare their centroiding performance with CCDs using the best available characteristics of each. We show that for sub-aperture binning of 6x6 and greater that noiseless detectors have a smaller centroid error at fluences of 60 photons or less, though the specific number is dependent on seeing conditions and the centroid algorithm used. We then present the status of a 256x256 noiseless MCP/Medipix2 hybrid detector being developed for AO.
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The design, simulation and characterization of Silicon Avalanche Photodiode (SAPD) that can be implemented with SILVACO TCAD tool are presented. This SAPD design used the diffusion of p-wells to create a low p layer doping density as the guard ring to prevent the premature breakdown at the edge of the device. The result demonstrated that the proper gap length between p-wells to create the guard ring allows SAPD to work in the Geiger mode. This showed that by developing a low-doped guard ring at the edge of the junction, it will reduce the electric field, minimize the avalanche current and the edge breakdown can be prevented. In this paper, the SAPD with square shape active area of 2 × 2 μm2 and low doped p-well guard ring has VBD of 27 V and avalanche current of 0.85 pA.
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An overview of photon counting detection using CMOS compatible Single Photon Avalanche Diodes (SPAD) will be presented. These SPADs have a planar structure, and are processed using CMOS technology. The most promising aspect of this technology is the potential for building large area arrays that can be operated in photon counting mode – without the read-out noise and bulkiness associated with low noise CCD cameras. Using the iAQC (integrated Active Quenching Circuit) produced by Micro-Photonics Devices, a low noise InGaAs/InAlAs APD will be characterized for photon counting. Finally, Characterization data from a photon counting module using Intevac's IPD's (Tube+APD hybrd) will be presented for photon counting at 1064nm.
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The goal of the CALDO experiments is to demonstrate Laser Guide Star technologies which can scale directly to a 100m diameter primary aperture, and which are not compromised by the cone-effect at very large telescope diameters. The laser guide star group at ESO and the adaptive optics group at Durham have proposed two different laser wavefront sensing methods designed to meet this goal. Though based on quite different physical principles, the two methods achieve their scalability through the use of a parallel sensing beam projected from the whole of the telescope primary mirror. They can therefore both be demonstrated by performing a scaled-down projection and sensing experiment on a smaller telescope. The CALDO experiments evaluate the ESO and Durham methods concurrently and provide a comparison with Natural Guide Star wavefront sensing, and with each other, without the uncertainty introduced into a separate evaluation by changing atmospheric conditions. The location for CALDO is the 4.2m William Herschel Telescope, which has the advantage of the GHRIL Nasmyth facility for adaptive optics experiments and which has already been used by the Durham group for shared-optics launch experiments with a laser guide star. We describe the ESO and Durham methods, the current progress on the experimental subsystems, and the projected timescales for the experiments.
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In the great majority of the cases, present astronomical observations are realized analyzing only first order spatial or temporal coherence properties of the collected photon stream. However, a lot of information is "hidden" in the second and higher order coherence terms, as details about a possible stimulated emission mechanism or about photon scattering along the travel from the emitter to the telescope. The Extremely Large Telescopes of the future could provide the high photon flux needed to extract this information. To this aim we have recently studied a possible focal plane instrument, named QuantEYE, for the 100 m OverWhelmingly Large Telescope of the European Southern Observatory. This instrument is the fastest photon counting photometer ever conceived, with an array of 100 parallel channels operating simultaneously, to push the time tagging capabilities toward the pico-second region. To acquire some experience with this novel type of instrumentation, we are now in the process of realizing a small instrument prototype (AquEYE) for the Asiago 182 cm telescope, for then building a larger instrument for one of the existing 8-10 m class telescopes. We hope that the results we will obtain by these instruments will open a new frontier in the astronomical observations.
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We have carried out a conceptual study for an instrument (QuantEYE) capable to detect and measure photon-stream statistics, e.g. power spectra or autocorrelation functions. Such functions increase with the square of the detected signal, implying an enormously increased sensitivity at the future Extremely Large Telescopes, such as the OverWhelmingly Large (OWL) telescope of the European Southern Observatory (ESO). Furthermore, QuantEYE will have the capability of exploring astrophysical variability on microsecond and nanosecond scales, down to the quantum-optical limit. Expected observable phenomena include instabilities of photon-gas bubbles in accretion flows, p-mode oscillations in neutron stars, and quantum-optical photon bunching in time. This paper describes QuantEYE, an instrument aimed to realize the just described science, proposed for installation at the ESO OWL telescope focal plane. The adopted optical solution is relatively simple and possible with actual technologies, the main constraint essentially being the present limited availability of very fast photon counting detector arrays. Also some possible alternative designs are described, assuming a future technology development of fast photon counting detector arrays.
Chapter
Investigative studies have designed concept instruments for a proposed 42 m European Extremely Large Telescope (E-ELT) facility suite. An ELT will aid, at its most basic level, detection of the faintest stellar sources and instrinsic features, and detailed quantitative analysis of relatively bright sources. The development of such a telescope thus plays to the strengths of high time resolution (HTR) detectors which provide single photon detection capabilities and/or extremely high refresh rates—they can maximize detection of faint sources through photon counting and they can cope with the high photon flux from relatively bright objects building up extremely high S/N. Specific considerations and fast detectors then need to be adopted into the ELT design to accommodate high time resolution astrophysics (HTRA) efficiently. No one instrument or detector can cover all HTRA timescales (nanoseconds to seconds and ‘slower’), and a dedicated facility HTRA instrument on the ELT is unlikely as yet, but chosen facility instruments can include HTRA options in their packages. Currently there are numerous HTRA options in existing telescope facilities around the world as well as many visiting HTRA instruments. This demonstrates an active HTRA community with worldwide support and interest in HTRA observation capabilities, which underscores the need for HTR capabilities to be designed into the ELT.
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A compact and flexible circuit for operating avalanche photodiodes in Geiger mode was designed, fabricated, and tested. A new voltage driver stage, based on fast n‐channel double‐diffused metal–oxide–semiconductor (DMOS) transistors in a bootstrap configuration, makes it possible to obtain quenching pulses up to 25 V amplitude and fast active reset of the detector. At 20 V excess bias voltage above the photodiode breakdown level, an overall deadtime shorter than 36 ns is attained. The avalanche pulse charge is minimized by means of a mixed passive–active quenching approach, thus reducing self‐heating and afterpulsing effects in the photodiode. A user‐controllable hold‐off time is available for further reducing the afterpulsing effect. The saturated counting rate of the circuit exceeds 25 Mcounts/s, but, by working with avalanche photodiodes with high breakdown voltage (250–400 V) and high avalanche current (10–40 mA), a practical limit is set at about 9 Mcounts/s by thermal effects in the detector. Gated‐detector operation with gate times down to 10 ns is provided. The suitability of the new active‐quenching circuit for the development of compact, all‐solid‐state instruments for high‐performance photon counting was verified in experimental tests. © 1996 American Institute of Physics.
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The properties of avalanche photodiodes and associated electronics required for photon counting in the Geiger and the sub-Geiger modes are reviewed. When the Geiger mode is used, there are significant improvements reported in overall photon detection efficiencies (approaching 70% at 633 nm), and a timing jitter (under 200 ps) is achieved with passive quenching at high overvoltages (20-30 V). The results obtained by using an active-mode fast quench circuit capable of switching overvoltages as high as 15 V (giving photon detection efficiencies in the 50% range) with a dead time of less than 50 ns are reported. Larger diodes (up to 1 mm in diameter) that are usable in the Geiger mode and that have quantum efficiencies over 80% in the 500-800-nm range are also reported.
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We describe the design of the ESO Adaptive Optics (AO) systems for the very large telescope interferometer (VLTI). We consider hereafter both the tip-tilt only corrections and the high order systems. The high order AO systems are designed for K-band operation on the Unit Telescopes (UT). The K-band UT beams will be combined with the 1.8m Auxiliary Telescopes (AT) operating with tip-tilt correction only, via ESO's Strap system. The UT-AO system will be hosted in the Coude' laboratory, with the deformable mirror inserted at the M8 location of the optical train. The wavefront sensor retains the option to be either in the Coude' lab, before the delay lines, or at the end of the beam combining path in the Interferometry laboratory, depending on the instrument attached and its use.
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The evolution of solid-state avalanche detectors of single optical photons is outlined and the issues for further progress are discussed. Physical phenomena that underlay the operation of the single-photon avalanche diodes (SPAD) and determine the performance are considered and their role is assessed (detection efficiency; dark-counting rate; afterpulsing; photon timing resolution; etc.). The main technological issues that hamper the development of detectors with wide sensitive area and of array detectors with high filling factor are illustrated. Silicon SPADs are the main focus of attention; infrared-sensitive SPADs in germanium and in compound semiconductors are also dealt with. The role of the active-quenching circuits (AQC) is assessed and the evolution is outlined up to integrated AQCs, which offer the prospect of monolithic integration of complete photon counter instruments.
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Geiger-mode avalanche photodiodes are interesting substitutes for conventional photomultiplier tubes in measurements of fast optical waveforms. In this paper we discuss the physical mechanisms involved in the detector operation and we clarify how these effects set a limit to the achievable timing performance. We show that a proper choice of the electric field profile is mandatory for the design of devices combining high quantum efficiency and timing resolution given by the ultimate transit time limit.
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A new single-proton avalanche diode (SPAD) with double-epitaxial silicon structure is presented. The device has a time response with short diffusion tail (270 ps time-constant), high resolution (45 ps FWHM, full-width at half maximum of the peak) and low noise, i.e. low-dark-count rate.
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A new silicon single-photon avalanche diode (SPAD) with epitaxial structure is presented. The carrier diffusion effect, which has plagued the time response of previous SPADs, is strongly reduced. The resolution obtained, less than 30 ps full width at half-maximum, is the highest so far reported in single-photon timing
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Single-photon detection by avalanche photodiodes with uniform breakdown over the junction area (single--photon avalanche diodes SPADs) is well known. The active quenching method, introduced by the authors, has been shown to avoid drawbacks of passive-quenching circuits and provide accurate operation of the devices. New active-quenching circuits are here presented. Dead times below 20 ns are obtained. A fast gating control acting directly on the photodetector has been developed, in view of timing studies with closely-spaced ultrashort light pulses.
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A monolithic circuit has been designed for active-quenching and active-reset of single-photon avalanche diodes (SPADs), which operate above the breakdown voltage V<sub>BD</sub> for detecting single photons. To the best of our knowledge, this is the first fully integrated circuit of this kind ever reported. It can operate with any available SPAD device, since it generates pulses high enough to quench detectors biased up to 20 V above V<sub>BD</sub>. The deadtime after each photon detection is adjustable; the minimum value is 50 ns, corresponding to 20 Mcounts/s maximum saturated photon-counting rate. The power dissipation is low (20-mW standby), suitable also for portable instruments. The small size and high reliability of the circuit make it possible to develop miniaturized detector modules and SPAD-array detector instruments. The circuit opens the path to new developments in many applications of photon counting, from DNA sequencing to ultrahigh-sensitivity imaging.