Method for the realization of a UVC imaging system based on a focal plane array of metal-semiconductor-metal photodetectors on the basis of an aluminum alloy with gallium oxide

Abstract

Method for the realization of a UVC imaging system based on a focal plane array of metal-semiconductor-metal photodetectors based on an aluminum alloy with gallium oxide. Metal-semiconductor-metal UVC photodetectors with metallic contacts in Ni and / or Au and / or Ti, characterized in that said photodetector comprises an aluminum alloy with Ga2O3 so as to give a broadened spectral response and / or shifted towards shorter wavelengths compared to a detector based on Ga2O3 only. The invention also relates to an imaging system based on a UVC focal plane array with an array of MSM photodetectors with metallic contacts in Ni and / or Au and / or Ti, based on (Al)Ga2O3 for the remote optical detection / localization / imaging of a fire, a corona discharge, a missile launch, ozone hole monitoring, gas detection.The invention also relates to UVC MSM photodetectors, designed on a substrate that is transparent in UVC so as to allow a retro-rear and thus facilitate the manufacture of flip chip devices which have higher yields compared to detectors with front illumination because reflections of light by front surface metal contacts are avoided.

Description

Title of the invention: Method for producing a UVC imaging system based on a focal plane matrix of metal-semiconductor-metal photodetectors based on an aluminum alloy with gallium oxide. TECHNICAL FIELD OF THE INVENTION

[0001] This invention provides the method of realizing a new optical imaging network in the UVC.

[0002] Among many potential applications, this imaging system could locate the start of fires more quickly.

[0003] Better remote optical detection is urgently needed to locate and more quickly extinguish the fires ravaging our planet. Since infrared detectors are prone to false alarms from surrounding heat sources, optical fire sensors typically couple sensors to the sun, which are not subject to such spurious signals. These are primarily vacuum tube photomultipliers (PMs) that are highly sensitive but bulky, fragile, expensive, and require high-voltage operation.

[0004] So far, semiconductor-based sensors have not been able to replace PMs because none of the current commercial options are inherently insensitive to sunlight, GaN requires an aluminum alloy, and Si & SiC require filters, resulting in low efficiency and a need for preamplifiers and / or high-voltage avalanche operation.

[0005] Recently, the inventors of the present invention developed revolutionary UVC sensors that were launched on a French cubesat mission in April 2023 [1, 3, 6-8, 11]. Based on a new generation semiconductor, Ga2O3, these sensors exhibit intrinsic insensitivity to sunlight and a strong spectral response. Therefore, they do not require solar filters, preamplifiers, or high operating voltages, resulting in significantly reduced mass, size, and cost compared to PMs. In qualification tests for use on small satellites, these sensors have also proven to be highly resistant to heat, cold, vibration, and radiation. STATE OF THE PRIOR ART

[0006] Deep Ultraviolet (DUV) detection systems have attracted great interest in recent years due to their wide range of potential applications, including chemical analysis, UV lamp sterilization monitoring, detectors of high-temperature flames, as well as receivers for ultraviolet communications, among others. Some of these applications, including high-temperature flame detectors and ultraviolet communications receivers, show virtually no noise caused by solar radiation, as most of the DUV radiation is absorbed by the ozone layer. (Ref: Avila-Avendano et al., in "Deep UV Sensors Enabling Solar-Blind Flame Detectors For Large-Area Applications" (IEEE Sensors Journal, 21, 13 (2021) 14815))

[0007] Conventional materials used in DUV detection systems include ultra-wide bandgap (UWBG) semiconductors, with a bandgap (Eg) much larger than the 3.4 eV of gallium nitride (GaN), gallium oxide (Ga2O3) (Eg 4.9eV), boron nitride, and diamond. These materials enable the fabrication of solar-insensitive DUV sensors with sensitivity values ​​up to 1.3x103 A / W for a ZnO / Ga2O3 microdot avalanche photodetector (APD). Integration of DUV detection systems with compatible low-cost, large-area circuit technologies is required to enable broader applications. An example is the focal plane array (FPA) for sun-insensitive DUV imagers, which has been realized only using multi-layer AlxGal-xN PIN photodiodes, packaged and discretely connected to commercially available CMOS readout ICs.This approach relies on high-end processes that are not compatible with large-area or low-cost applications.

[0008] Further technological advances are needed to make UV detection technologies compatible with low cost and large area flame detection. Flame detectors require a high DUV / visible rejection ratio (RR) to avoid false alarms, as most of these detectors operate under artificial or natural lighting. Currently, photomultiplier tubes are the most commonly used devices for flame detection in UVC; however, these devices are fragile, expensive, bulky, difficult to scale, and require high operating voltages.

[0009] To address some of these technological bottlenecks, flame detectors using UWBG semiconductors are being investigated as alternatives. For example, AlGaN PIN photodiodes on sapphire fabricated by lateral epitaxial growth with a sensitivity of 0.1 A / W at a wavelength of 270 nm have been demonstrated as flame detectors. In addition, Schottky photodiodes based on single-crystal gallium oxide fabricated using the floating zone (FZ) method have also been demonstrated for flame detection applications. This photodetector exhibited a sensitivity of 37x103 A / W at a wavelength of 250 nm. Flame detection was demonstrated when the device was connected to a commercial amplifier based on conventional CMOS electronics. Although these devices have demonstrated flame detection capabilities using UWBG semiconductors, they are not compatible with low-cost, large-area applications due to the use of high-temperature growth methods that are incompatible with conventionally used CMOS electronics for signal amplification.

[0010] In a rapidly growing market for UV sensors, with an estimate of reaching $2.7 billion by 2024, UWBG semiconductor-based detectors have hardly found their place in real-world systems and imaging that use UV detection (e.g., onboard spacecraft or for flame detection) (Ref.: Kalra et al. explain in their article "The road ahead for ultrawide bandgap solar-blind UV photodetectors" (J. Appl. Phys. 131, 150901 (2022)) ) Indeed, CCD- and CMOS-based UV imagers dominate this market, despite their complexities related to additional filters, reduced efficiency, and weight. Research on UWBG UV detectors has been, until now, mainly confined to the academic sphere.

[0011] Although there is a significant volume of reports in the literature on all aspects of material growth and device development for UWBG photodetectors, studies on focal plane arrays (FPAs) and their integration with readout integrated circuits (RoICs) are relatively underexplored. There are even fewer reports on the investigation of reliability and yield, aging / wearout testing, radiation hardening, and failure mechanisms of these device technologies. This gap in the literature poses a significant barrier to the commercial and strategic implementation of real-world systems using UWBG-based deep DUV sensors for imaging. Moreover, while AlGaN / GaN HEMTs are rapidly entering the market for other applications, the strategic sector of deep UV AlGaN detectors remains confined to the academic research domain.Since the aluminum content in AlGaN can be modulated to adjust the band gap and, consequently, the cutoff wavelength between 200 and 365 nm, there are several studies on the demonstration of AlGaN-based UVB detectors as well. However, for blind detection in sunlight (<290 nm), the aluminum content in AlGaN must be at least 40%, which poses some challenges from a materials development perspective. Epitaxy of AlGaN with high aluminum content (>40%) is itself non-trivial with respect to controlling background impurity concentration, doping, strains, dislocation densities, and other defects. such as V-wells, all of which have a substantial influence on device performance.

[0012] Moreover, p-type doping continues to represent a great technological difficulty, given that the ionization energy of Mg (used mainly for p-doping) is quite high for AlGaN. In fact, even the study and development of a highly conductive AlGaNn-type, with a high aluminum content, still remains an important subject of research.

[0013] For sun-blind UV detectors, sapphire is more commonly used than other substrates due to the fact that sapphire is transparent to deep UV (>190 nm), allowing backside illumination (backlighting) of the devices, which is necessary for FPAs in flip-chip configuration. Low lattice mismatch with AlGaN, lower cost (compared to SiC and AlN), good growth control, and large-scale manufacturing capability also favor the choice of sapphire. In addition to what the two reviews above describe, the authors (David, Rogers et al (Proc, of SPIE Vol. 12422 (2023) 07-1)) demonstrated in 2023 excellent results on the efficiency, reliability, robustness, stability, age / climate testing, and failure mechanisms of discrete Ga2O3 UVC photodetectors.Subsequently, the sensors demonstrated TRL9 technology readiness level (and radiation hardening) during their successful deployment in space aboard a cubesat mission in April 2023. To our knowledge, this is the first real-world TRL9 deployment of Ga2O3 photodetectors.

[0014] This invention relates to the development of a Ga2O3-based UVC focal plane array for optical fire detection / localization. It provides filter-free and pre-amplification-free operation, with a maximum response / width specifically optimized for fire detection. Optical, electronic and image processing solutions will enable exploitation of the extreme sensitivity. Comparable UVC imaging arrays are not commercially available, and they will enable a number of space and terrestrial applications, such as UV astronomy, missile launch detection / localization, free-path gas detection / localization and various inspection systems. Disclosure of the Invention

[0015] The present invention relates to the method of manufacturing a UVC imaging system for, for example, the optical detection / localization of the start of fires.

[0016] To do this, the invention proposes a focal plane matrix of UVC Metal-Semiconductor-Metal type photodetectors with metal contacts, made of Ni and / or Au and / or Ti, characterized in that it comprises an aluminum alloy with Ga2O3 so that to give a broadened and / or shifted spectral response towards shorter wavelengths compared to a Ga2O3-only detector.

[0017] Furthermore, this MSM UVC photodetector with Ni and / or Au and / or Ti metal contacts is designed to provide partially Schottky and partially Ohmic contacts to both trap charge holes at the metal-semiconductor interface (to increase gain) and also to benefit from a low dark signal, fast response and high photoconductive gain.

[0018] In addition, the above UVC MSM photodetector array is designed on a substrate that is transparent in UVC (e.g. sapphire or quartz) to allow backlighting and the fabrication of flip chip devices. This increases the efficiency of the photodetectors by eliminating light reflections from the metal contacts that are responsible for the drop in efficiency when the light arrives from the front face.

[0019] According to features of the invention, the MSM UVC photodetectors, based on (Al)Ga2O3 have a decreasing aluminum concentration gradient during growth, (by the deposition conditions), which will make it possible to capture a broader spectrum of UVC light.

[0020] This result can be achieved using several approaches. For example, during growth by modulating the concentration of the elements used (gradient created by the deposition conditions such as the change in the aluminum flux during Molecular Beam Epitaxy, a precursor flux for aluminum during Chemical Vapor Phase Deposition (CVD), a precursor flux for aluminum in MOCVD (Metal Organic Chemical Beam Deposition), a different Al content in the targets used by physical evaporation (Sputtering, Ion Beam Deposition) or even by laser ablation (Puise Laser Deposition), Atomic Layer Deposition). Another example concerns the use of post-growth heat treatment or a high deposition / annealing temperature / duration to promote the diffusion of aluminum from the A12O3 (sapphire) substrate.Another approach would be the use of an Al-rich underlayer (such as Al2O3 or Al-0 or Al-Ga-N) on a UV-transparent substrate other than sapphire or not. Another approach would be a mechanical stacking of atomic sheets with different concentrations.

[0021] The invention also relates to a flip chip MSM UVC photodetector, based on a thin layer (between 2 nanometers and 1 micron in thickness) of (Al)Ga2O3 created with a decreasing gradient of (Al) with thickness, thanks to the growth conditions of the materials and / or a post-growth heat treatment, which will allow the shallower UVC light to transmit further into the layer in order to arrive closer to the upper surface (where the metal contacts are located) and thus provide a wider wavelength detection window and thus more efficient and more complete UVC detection.

[0022] The invention also relates to an imaging system based on a UVC focal plane array based on an array of (Al)Ga2O3-based MSM photodetectors for remote optical detection / location / imaging of fire, corona discharge, missile launch, leak triggering, ozone hole monitoring, gas detection. BRIEF DESCRIPTION OF THE FIGURES

[0023] [Fig.l] illustrates inter-digitized transducer (IDT) metal-semiconductor-metal (MSM) photodetectors fabricated on transparent sapphire substrates;

[0024] [Fig.2] shows the flip chip bump bonding die fixture

[0025] [Fig.3] Shows the uncalibrated composition profile by GDMS for gallium and aluminum from a Ga2O3 layer grown on a sapphire substrate;

[0026] [Fig.4] A diagram of the proposed detector structure and the architecture of the assembly

[0027] DETAILED DESCRIPTION OF THE DRAWINGS

[0028] [Fig.2] shows: 1) electrical contact with the individualized chip, made via contact pads (e.g., In / Au eltectique) on the metal front electrode, followed by flipping the chip before bonding to the base. The light in this case passes through the transparent substrate, which eliminates reflection losses due to the metal electrodes. This process is simpler and more robust than front illumination and wire bonding. Moreover, it does not require expensive wire bonding equipment. 2) Attaching the chip to a packaging carrier is already part of the process, thus reducing the number of process steps.

[0029] [Fig. 3] presents depth profiles by glow discharge mass spectrometry (GDMS) for Ga2O3 grown on sapphire at high temperature. The graph shows that there is significant diffusion of aluminum from the substrate into the Ga2O3 layer, which increases the band gap width near the substrate. DETAILED DESCRIPTION OF THE INVENTION

[0030] The aim of the present invention is to construct = an optical imaging system in the UVC (which could, for example, be used for early detection / localization in low Earth orbit of the ignition of fires on Earth).

[0031] The system is based on a focal plane array (FPA) of innovative (Al)Ga2O3-based UVC sensors. Such individual sensors have been successfully tested for a French cubesat mission to measure the Earth's radiation budget ("INSPIRESAT 7" launched with Space X in April 2023) [1, 3, 6-8, 11].

[0032] A second innovative aspect is to design detectors with increased gain / efficiency and panchromatic response (in the UVC) in order to maximize sensitivity and allow miniaturization of the FPA.

[0033] A third innovative aspect is to incorporate innovative flip-chip hybridization to maximize the signal (no front-contact reflection losses), simplify manufacturing and strengthen the system (no fragile wire bonds).

[0034] A fourth innovative aspect is to develop UV optics adapted for maximum coupling and precise positioning of light.

[0035] Better remote optical detection is urgently needed to locate and extinguish fires ravaging our planet more quickly. Since infrared detectors are subject to spurious signals from surrounding heat sources, optical fire sensors are usually coupled with UVC sensors (insensitive to solar radiation) which are not subject to such false alarms. Comparable UVC imaging arrays are not present in the academic literature and they are also not commercially available. They will open up many possibilities for space and terrestrial applications, such as UV astronomy, missile launch detection / localization, free-travel gas detection / localization and various inspection systems.

[0036] The technical and functional requirements here relate to the ability to create a compact solid-state UVC imaging array with a good solar rejection ratio, good robustness, reasonable refresh time (in the millisecond range).

[0037] Furthermore, the interface requirements involve: (a) a novel flip-chip connection to a commercial imaging integrated circuit and (b) electronic and software interfaces to the ROIC.

[0038] In addition, environmental requirements include minimizing the use of toxic or critical materials in the manufacture / use of components.

[0039] The benefit to the user is that there is currently no good commercial solution for UVC imaging. This revolutionary technology would enable the development of many important applications, such as UV astronomy, missile launch detection / localization, free-path gas detection / localization; flame / furnace monitoring, off-line communications, corona detection and various inspection systems.

[0040] In particular, the potential impact on society of reducing fire damage (through earlier detection / extinction) is quite dramatic in terms of forests lost, farmland destroyed, housing and infrastructure burned, and reduced greenhouse gas emissions (it is It is now accepted that forest fires produce a comparable amount of greenhouse gases as that emitted by all the motor vehicles in the world. List of cited documents

[0041] 1. Dynamical properties and performances of B-Ga2O3 UVC photodetectors of extreme solar blindness:

[0042] L. Damé, L. Conan, C. De Santi, A. Caria, M. Buffolo, M. Meneghini, P. Maso, C. Dias, H. Ghorbel, P. Gilbert, M. Meftah, P. Bove, V. Sandana, D. Rogers, F. Teherani Proc, of SPIE Vol. 12422 (2023) 07-1.

[0043] 2. Investigation of Enhanced Heteroepitaxy and Electrical Properties in Kappa- Ga2O3 due to Interfacing with [3-Ga2O3 Template Layers J. Lee, L. Gautam, FH Teherani, EV Sandana, P. Bove, DJ Rogers and M.Razeghi

[0044] Phys. Stat. Solidi. a (2023) 2200559.

[0045] 3. Realization, Calibrations and Spatialization of B-(Al)Ga2O3 UVC Photodetectors of Extreme Solar Blindness for Space Observations ; Proc, of 8th International Conference on Sensors Engineering & Electronics Instrumentation Advances, Corfu (2022).

[0046] 4. Effect of high-energy electron irradiation on the electronic properties of beta gallium oxide ; T.-H. Dang , M. Konczykowski , VI Safarov , E. Hammou , LR Vega , N. Ollier , R. Grasset , A. Alessi , H.-J. Drouhin , Jaffresh H , Davydov VY , Wolos A , DJ Rogers , Sandana VE , Bove P H , Tehran FH ; 07-1 (2022) 12002 Proc, of SPIE.

[0047] 5. Microstrip Array Ring FETs with 2D p-Ga2O3 Channels Grown by MOCVD M . Razeghi , J. Lee , L. Gautam , J.-P. Leburton , FH Tehran , PK Amiri , M.Grayson , VP Dravid & D. Pavlidis Photonics 8 (2021) 578 .

[0048] 6. Préparation & Characterization of [3-Ga2O3-based Photodetectors for UV Détection Applications ; H. Ghorbel, L. Damé, M. Meftah, X. Arrateig, F. Bouyssou, I. Sidi-Boumeddine, P.Gilbert, P. Maso, D. Rogers, P. Bove, V. Sandana, F. Teherani Proc, of 7th International Conférence on Sensors Engineering & Electronics Instrumentation Advances, Mallorca (2021).

[0049] 7. Performances and Calibrations of New Disruptive UVC Sensors for New Space Applications ; I. Sidi Boumeddine, F. Bouyssou, L. Damé, H. Ghorbel, X. Arrateig, M. Meftah, P.Gilbert, P. Maso, D. Rogers, P. Bove, V. Sandana & F. Teherani ; Proc, of 7th International Conférence on Sensors Engineering & Electronics Instrumentation Advances, Mallorca (2021).

[0050] 8. Development and Simulated Environment Testing of [3-(Al)Ga2O3-based Photodetectors for Space-based Observation of the Herzberg Continuum X. Arrateig, D. Rogers, P. Maso, F. Bouyssou, I. Sidi-Boumeddine, W. El-Huni, H. Bouhnane, Y. Sama, P. Bove, S. Le Gall, A. Brezart-Oudot, H. Ghorbel, P. Gilbert, V. Sandana; Tehran, S. Gautier, A. Darga, Z. Djebbour, A. Ougazzaden; Proc, of SPIE 11858(2021)1185813-1.

[0051] 9. Sharp / Tuneable UVC Selectivity and Extreme Solar Blindness in Nom Undoped Ga2O3 MSM Photodetectors Grown by Pulsed Laser Deposition ; http: / / dx.doi.org / 10.1037 / 0033-295X.111.1.103 Rogers, A. Courtois, FH Teherani, VE Sandana, P. Bove, X. Arrateig, L. Damé, P. Maso, M. Meftah, W. El Huni, Y. Sama, H. Bouhnane, S. Gautier, A. Ougazzaden & M. Razeghi Proc. SPIE 11687 (2021) 116872D-1.

[0052]

[0052] A walk on the frontier of energy electronics with power ultra-wide bandgap oxides and ultra-thin neuromorphic 2D materials; A. Perez-Thomas, E. Chikoizde, D. Rogers, JA Garrido Proc. SPIE 11687 (2021) 116871Y-1.

[0053] 11. UVSQ-SAT, a Pathfinder CubeSat Mission for Observing Essential Climate Variables M. Meftah, L. Damé, P. Keckhut, S. Bekki, A. Sarkissian, A. Hauchecorne, E. Bertran,JP Carta, D. Rogers, S. Abbaki, C. Dufour, P. Gilbert, L. Lapauw, AJ Vieau, X.Arrateig, N. Muscat, P. E. Bonave, Sanda, Teherani, T. Feher. G. Pradel, M. Mahé, C.Mercier, A. Paskeviciute, K. Segura, AB Alba, A. Aboulila, L. Chang , A. Chandran,PR. Dahoo and A. Bui Remote Sens. 12, (2020) 92.

[0054] 12. Red Luminescence in H-doped [3-Ga2O3 TT Huynh, E. Chikoidze, M. Zakria, Y. Dumont, FH Teherani, EV Sandana, P.Bove, DJ Rogers, MR Phillips, J. Ton-That Phys. Freeze. Materials 4, 085201 (2020).

[0055] 13. Solar-blind Conducting Gallium Oxide Enables Record Bulk Photovoltaic Effect A. Perez-Tomas, E. Chikoidze, Y. Dumont, M. R. Jennings, Y. Kurtulug, G. Catalana, M.Lira-Cantu, C. Ton -That, F. H. Teherani, V. E. Sandana, P. Bove and D. J. Rogers Materials Today Energy, 14 (2019) 100350.

[0056] 14. Puzzling robust 2D metallic conductivity in undoped beta-Ga2O3 thin Films; E. Chikoidze, D.J. Rogers, F.H. Teherani, C. Rubio, G. Sauthier, H. Von Bardeleben, T.Tchelidze, C. Ton-That, A. Fêlions, P. Bove, E. Sandana, Y. Dumont & A. P. Tomas Materials Today Physics 8 (2019) 10 - 17.

[0057] 15. Wide and ultra-wide bandgap oxides: where paradigm-shift photovoltaics meets transparent power electronics A. Pérez-Tomâs, E. Chikoidze, M. R. Jennings, S. A. O. Russell, F. H. Teherani, P.Bove, E. V. Sandana and D. J. Rogers Proc, of SPIE 10533 (2018) 105331Q-1.

[0058] 16. A Review of the Growth, Doping & Applications of beta-Ga2O3 thin films; M. Razeghi, J.-H. Park , R.McClintock , D. Pavlidis , FH Tehran , DJ Rogers , B . A.Magill, GA Khodaparast, Y. Xu, J. Wu and VP Dravid ; Proc, of SPIE 10533 (2018) 105330R-1.

[0059] 17. The New Oxide Paradigm for Solid State Ultraviolet Photodetectors ; DJ Rogers , FH Tehran , Sandana VE , Arrateig X , Bove P , Razeghi M , Clintock R , Frisch E , and Harel S ; Proc, of SPIE 10533 (2018) 105331P-1.

[0060] 18. A Study into the Impact of Sapphire Substrate Orientation on the Properties of Nominally-Undoped Ga2O3 Thin Films Grown by Pulsed Laser Deposition ; FH Teherani, DJ Rogers, VE Sandana, P Bove, C Ton-That, LLC Lem, E Chikoidze, M Neumann-Spallart, Y Dumont, T Huynh, MR Phillips, P Chapon, R McClintock & M Razeghi

Claims

Claims

1. UVC Metal-Semiconductor-Metal (MSM) photodetector based on Ga2O3 semiconductor, with metal contacts made of Ni and / or Au and / or Ti, characterized in that it comprises an aluminum alloy with the Ga2O3, so that there is a broadened and / or shifted spectral response towards shorter wavelengths compared to a detector based on Ga2O3 only.

2. A metal contact UVC MSM photodetector according to claim 1, characterized in that the charge holes are trapped at the metal-semiconductor interface in order to increase the gain and benefit from a low dark signal, a fast response and a high photoconductive gain.

3. MSM UVC photodetectors, according to claim 1 characterized in that it is designed on a substrate which is transparent in UVC with backlighting to facilitate the fabrication of flip chip devices for higher efficiency compared to detectors with front-side illumination.

4. MSM UVC photodetectors, according to claim 1 characterized in that said (Al)Ga2O3 based photodetector has a decreasing aluminum concentration gradient in the material in thickness, created by deposition conditions such as an aluminum flow in the MBE, a precursor flow for the aluminum in the MOCVD or a high deposition / annealing temperature / duration which promotes the diffusion of aluminum from the Al2O3 (sapphire) substrate which will allow a broader spectrum of UVC light to be captured.

5. A flip chip MSM UVC photodetector according to claim 3 and 4 characterized in that it is based on a thin layer, between 2 nanometers and 1 micron in thickness of (Al)Ga2O3 and is created with a decreasing gradient of (Al) with thickness, through the deposition conditions, allowing shallower UVC light to transmit further into the layer to arrive closer to the upper surface with the metal contacts and providing broadband UVC detection.

6. A UVC focal plane array based imaging system based on an MSM photodetector array according to any one of claims 1 to 5 for remote optical detection / location / imaging of a fire, corona discharge, nuclear launch missile, ozone hole monitoring, gas detection.

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