Megapixel Array Research Articles

Design and fabrication of single photon detector with ultra-large area superconducting nanowire array

<sec>Superconducting nanowire single-photon detector (SNSPD) is one of the most mainstream single-photon detectors at present, which possesses excellent comprehensive performance, including low time jitter, high efficiency, low dark count, and wide spectrum. However, the traditional single-pixel SNSPD suffers a lack of spatial resolution and a small photosensitive surface, which becomes a bottleneck associated with optical coupling efficiency. In addition, a single-pixel detector has no ability to resolving the photon number, whose working speed cannot be further improved due to the existence of dead time. While array devices can make up for the above deficiencies. Therefore, the development of a large-area SNSPD array is the key to free-space photon detection and other applications. In recent years, the relevant researches have been conducted and great progress has been achieved. However, the large-area SNSPD array is facing some intractable problems, including complex process, low yield, and difficult fabrication, owing to the photosensitive surface consisting of a large number of superconducting nanowires. Photons imaging is verified with this device. At present, in the existing studies mainly used is the three-dimensional technology with complicated process steps to fabricate large array SNSPDs. How to simplify the process has become a research focus.</sec><sec>In this work, we design an ultra-large area nanowire array structure and propose an innovative plane process. Taking advantage of the property that the electron beam resists HSQ (hydrogen silsesquioxane polymer) forming a silicon oxide electrical isolation layer after exposure, we fabricate a large array SNSPD with a simplified two-dimensional process and realize dimensionality reduction for the traditional three-dimensional process of a multilayer structure. By measurement in parallel, the devices enjoy high yield with no bad points found. In addition, a full-superconducting electrode is adopted in our design to reduce the thermal effect of resistors. We add series and parallel resistors in the pixels to divide the bias current evenly and expand the array scale optionally. At the same time, we also offer the design details of array SNSPDs, the related simulation of hot spots to verify the rationality of the design, the optimization of the preparation conditions of array devices, measurement scheme formulation, and other related work.</sec><sec>This work provides an idea for designing and fabricating ultra-large array SNSPD, which is expected to be applied to the fabrication of megapixel array SNSPDs. Combined with an efficient readout circuit, a focal plane photon detection and imaging system with both a large field of view and high sensitivity can be realized.</sec>

Design and fabrication of large-area superconducting nanowire single photon detector arrays

Superconducting nanowire single-photon detectors (SNSPDs) are currently one of the most mainstream single-photon detectors with excellent comprehensive performance, including low time jitter, high efficiency, low dark count and wide spectrum. However, the traditional single-pixel SNSPD suffers from a lack of spatial resolution and a small photosensitive surface, which creates bottlenecks associated with optical coupling efficiency. In addition, a single-pixel detector does not have the photon number resolution ability, whose working speed cannot be further improved due to the existence of dead time. In this case, array devices can make up for the above deficiencies. Therefore, the development of a large-area SNSPD array is the key to free-space photon detection and other applications. In recent years, experimental groups at home and abroad have started relevant research and have made great progress. However, the large-area SNSPD array faces intractable problems, including complex processes, low yield and difficult fabrication, owing to the photosensitive surface consisting of large amounts of superconducting nanowires. At present, the existing studies mainly use three-dimensional technology with complicated process steps to fabricate large array SNSPDs. How to simplify the process has become a research focus.<br>In this paper, we design a large-area nanowire array structure and propose an innovative plane process. Taking advantage of the property that the electron beam resists HSQ forming a silicon oxide electrical isolation layer after exposure, we fabricate a large array SNSPD with a simplified two-dimensional process and realize dimensionality reduction for the traditional three-dimensional process of a multilayer structure. By measurement in parallel, the devices enjoy high yield with no bad points found. In addition, a fully superconducting electrode is adopted in our design to reduce the thermal effect of resistors. We add series and parallel resistors in the pixels to divide the bias current evenly and expand the array scale optionally. At the same time, we also offer the design details of array SNSPDs, the related simulation of hot spots to verify the rationality of the design, the optimization of the preparation conditions of array devices, measurement scheme formulation and other related work.<br>This work provides an idea for the design and fabrication of ultra-large array SNSPDs, which is expected to be applied to the fabrication of megapixel array SNSPDs. Combined with an efficient readout circuit, a focal plane photon detection and imaging system with both a large field of view and high sensitivity will be realized.

Organic photodetectors with frustrated charge transport for small-pitch image sensors

We demonstrate a frustrated organic photodetector (F-OPD) that utilizes frustrated charge-transport to quench forward-bias current and provide a low-current, light-independent OFF state. Photocurrent is collected efficiently with −3 V reverse-bias recovering the sensitive OPD response with >10-bit dynamic range. This intrinsic switching mechanism eliminates the need for thin-film transistors (TFTs) to provide readout control in high-resolution image sensors. Eliminating TFTs simplifies fabrication processing, improves fill-factor, and enables higher resolution image sensors on nonplanar, stretchable, or large-area substrates for a variety of imaging applications. We simulate image sensors and show that the performance is limited by the OFF state uniformity experimentally observed across 45 devices. We simulate performance in a 900-pixel array and show that the demonstrated F-OPDs can scale into megapixel arrays with a noise-equivalent power of <0.6 mW/cm2 and a dynamic range of >6-bits; better uniformity can substantially improve this performance for large arrays.

Massively Parallel Coincidence Counting of High-Dimensional Entangled States

Entangled states of light are essential for quantum technologies and fundamental tests of physics. Current systems rely on entanglement in 2D degrees of freedom, e.g., polarization states. Increasing the dimensionality provides exponential speed-up of quantum computation, enhances the channel capacity and security of quantum communication protocols, and enables quantum imaging; unfortunately, characterizing high-dimensional entanglement of even bipartite quantum states remains prohibitively time-consuming. Here, we develop and experimentally demonstrate a new theory of camera detection that leverages the massive parallelization inherent in an array of pixels. We show that a megapixel array, for example, can measure a joint Hilbert space of 1012 dimensions, with a speed-up of nearly four orders-of-magnitude over traditional methods. The technique uses standard geometry with existing technology, thus removing barriers of entry to quantum imaging experiments, generalizes readily to arbitrary numbers of entangled photons, and opens previously inaccessible regimes of high-dimensional quantum optics.

MKID digital readout tuning with deep learning

Microwave Kinetic Inductance Detector (MKID) devices offer inherent spectral resolution, simultaneous read out of thousands of pixels, and photon-limited sensitivity at optical wavelengths. Before taking observations the readout power and frequency of each pixel must be individually tuned, and if the equilibrium state of the pixels change, then the readout must be retuned. This process has previously been performed through manual inspection, and typically takes one hour per 500 resonators (20 h for a ten-kilo-pixel array). We present an algorithm based on a deep convolution neural network (CNN) architecture to determine the optimal bias power for each resonator. The bias point classifications from this CNN model, and those from alternative automated methods, are compared to those from human decisions, and the accuracy of each method is assessed. On a test feed-line dataset, the CNN achieves an accuracy of 90% within 1 dB of the designated optimal value, which is equivalent accuracy to a randomly selected human operator, and superior to the highest scoring alternative automated method by 10%. On a full ten-kilopixel array, the CNN performs the characterization in a matter of minutes — paving the way for future mega-pixel MKID arrays.

Thermal detectors of uncooled multi-element infrared imaging arrays. I. Thermally insulated elements

The current status of the list of elements of uncooled infrared (IR) imaging arrays based on thermal insulation of their sensors and on accumulation of heat in the element volume during the time necessary for taking one frame is considered. Specific features of operation and the structure of resistive microbolometers and pyroelectric elements are described, as well as typical parameters of these elements. Prospects of improving the parameters of thermally insulated sensors of megapixel arrays are considered. It is noted that the main factor limiting further improvement of the parameters of pixels in IR imaging arrays and increasing the size of the latter is the value of the thermal resistance between the sensor and the substrate. At the modern level of technology development, the thermal resistance has actually reached the limiting value. Another physical principle of operation of IR detectors is required for a further increase in the sensitivity of sensors, a decrease in their response time, and an increase in the size of uncooled megapixel IR arrays; this principle should not include the necessity of thermal insulation of IR detectors. The operation principle based on using pyrotechnical effects will be considered in the second part of the paper.

New AC-Powered SFQ Digital Circuits

Recent progress of Reciprocal Quantum Logic (RQL) has renewed interest in AC powering of superconductor digital circuits, which had been abandoned since the famous IBM project of 1970s. In this work we propose and demonstrate new AC-biased Single Flux Quantum (SFQ) circuits, and search for synergy of AC and currently dominating DC biasing schemes. As the first step, we suggest an on-chip AC/DC converter capable of feeding a few DC-biased gates surrounded by their AC-biased counterparts. As the second step, we introduce and present the first successful demonstration of a new AC-powered circuit - an 8192-bit shift register with over 32,800 Josephson junctions (JJs) and JJ density of about 6x$10^5$ JJ per $cm^2$. We suggest a few niche applications for this type of AC-biased circuits, not requiring high clock rates. E.g., these, scalable to millions of JJs per chip, circuits can serve as a convenient benchmark for new SFQ fabrication technology nodes, allowing the operating margins of individual cells to be extracted and, thus, 'visualize' individual fabrication defects and flux trapping events. The circuit can also be developed into a mega-pixel imaging array for a magnetic field microscope.

Resolution analysis in computational imaging with patterned illumination and bucket detection.

In computational imaging by pattern projection, a sequence of microstructured light patterns codified onto a programmable spatial light modulator is used to sample an object. The patterns are used as generalized measurement modes where the object information is expressed. In this Letter, we show that the resolution of the recovered image is only limited by the numerical aperture of the projecting optics regardless of the quality of the collection optics. We provide proof-of-principle experiments where the single-pixel detection strategy outperforms the resolution achieved using a conventional optical array detector for optical imaging. It is advantageous in the presence of real-world conditions, such as optical aberrations and optical imperfections in between the sample and the sensor. We provide experimental verification of image retrieval even when an optical diffuser prevents imaging with a megapixel array camera.

Solar magnetic fields as revealed by Stokes polarimetry

Observational astrophysics started when spectroscopy could be applied to astronomy. Similarly, observational work on stellar magnetic fields became possible with the application of spectro-polarimetry. In recent decades there have been dramatic advances in the observational tools for spectro-polarimetry. The four Stokes parameters that provide a complete representation of partially polarized light can now be simultaneously imaged with megapixel array detectors with high polarimetric precision (0.001% in the degree of polarization). This has led to new insights about the nature and properties of the magnetic field, and has helped pave the way for the use of the Hanle effect as a diagnostic tool beside the Zeeman effect. The magnetic structuring continues on scales orders of magnitudes smaller than the resolved ones, but various types of spectro-polarimetric signatures can be identified, which let us determine the field strengths and angular distributions of the field vectors in the spatially unresolved domain. Here we review the observational properties of the magnetic field, from the global patterns to the smallest scales at the magnetic diffusion limit, and relate them to the global and local dynamos.

Delta-doped electron-multiplied CCD with absolute quantum efficiency over 50% in the near to far ultraviolet range for single photon counting applications

We have used molecular beam epitaxy (MBE) based delta-doping technology to demonstrate nearly 100% internal quantum efficiency (QE) on silicon electron-multiplied charge-coupled devices (EMCCDs) for single photon counting detection applications. We used atomic layer deposition (ALD) for antireflection (AR) coatings and achieved atomic-scale control over the interfaces and thin film materials parameters. By combining the precision control of MBE and ALD, we have demonstrated more than 50% external QE in the far and near ultraviolet in megapixel arrays. We have demonstrated that other important device performance parameters such as dark current are unchanged after these processes. In this paper, we briefly review ultraviolet detection, report on these results, and briefly discuss the techniques and processes employed.

Self-Localizing Stabilized Mega-Pixel Picoliter Arrays with Size-Exclusion Sorting Capabilities

We report on a liquid self-localizing process capable of producing Mega-pixel arrays of picoliter volumes on a 1 cm(2) area, within seconds, for high throughput sampling. The chip is based on principles of spatially varying wetting and stabilization. The key is to develop differential surface contact regions, which lead to both localization of the solution and increasing the surface adsorption energy to further pin the liquid to the surface, as highlighted by other studies. By exploiting surface roughness for enhanced wettability, we demonstrate wetting of wells with the aspect ratio of 100. The high precision of reactive ion etching (RIE) of silicon substrates allows for an extremely reproducible method of preparing the array of identical well structures and increased contact area to increase surface adsorption in the wells. "Dynamic wetting" is then readily achieved through inducing contact line instability by simply moving a drop of liquid on the top surface of the array. Liquid samples self-localize into the array pattern with the associated liquid flow leading to self-localization of suspended particles or analyte. The resulting picoliter volumes are both spatially ordered and stable for long periods of time, even for such small volumes, to permit selective measurements of the contents. This development will be particularly important in the assembly of the massive amounts of crystalline particles needed for atomically resolved structural dynamics using the latest advances in high number density electron and X-ray sources.

Functionality, Yield and Reliability Analysis of SiGe Micro-mirrors using Automated Optical Measurement Techniques

This paper discusses optical systems for automatic, wafer or chip level measurements of metrology, functional yield and reliability of MEMS. The functionality of the systems is demonstrated on megapixel arrays of SiGe micro-mirrors. The back-bone of the systems is formed by existing commercial systems, but home-developed procedures and software were written to extend their functionality and applicability.

Development of an ultrafast single photon counting imager for single molecule imaging.

We have begun developing an innovative ultra-fast single-photon counting imager which comprises a mega-pixel CMOS array and a newly-designed Image Intensifier. It is expected to have single photon sensitivity with 100 psec time resolution, operational at a total counting rate exceeding 1MHz. The readout is based on dead-time-free flash ADC, running at 1-2GS/s, followed by a FPGA for real-time parallel data processing. Such a device has not been realized before and is expected to revolutionize time-resolved fluorescence imaging and spectroscopy from a single-molecule to whole animal level. To evaluate the design principle, an Image Intensifier with a GaAsP photocathode (>40% quantum efficiency at 400-600 nm) followed by double MCP was evaluated together with an existing CMOS camera. In our future design, the image from CMOS Camera will be combined with the MCP output, followed by a set of FPGA and CPU for real time data processing. This stream line method will allow ultra fast single-photon counting with 100 psec time resolution and 20 µm position resolution (1M pixel imaging). In this paper, we present the design principle and preliminary results on its performance. Our future plan and the design goals are also described.

Les nouvelles générations de détecteurs infrarouge à base de HgCdTe

The technology of very high performance cooled infrared detectors made with HgCdTe has progressed continuously for ten years and reached today an industrial maturity that allows the production of large size arrays at a more and more reasonable cost. At the same time, new prototypes of more complex sensors have appeared (megapixel arrays, multicolour arrays, high definition long linear arrays, … ) that show the strong potentialities of this very high performance technology. This paper presents the technology developed in France and gives the state of the art of products available in industry; it then focuses on some very recent realizations of advanced prototypes made at LETI (dualband arrays, megapixel arrays, … ). To cite this article: G. Destefanis, C. R. Physique 4 (2003).

Superconducting electronics requirements for single-photon, energy resolving detectors

Development of single photon sensors capable of determining the energy ("color") of each photon incident on a pixelated focal plane in real time is a central activity of many groups worldwide developing state-of-the-art hardware for the space astrophysics community. Terrestrial applications in materials analysis are also being targeted. The most successful class of approaches uses "hot-electron" microbolometers in which the energy of the photon elevates the electronic temperature in a metallic absorber and a dedicated thermometer measures this excursion. In a class of devices called thermoelectric microbolometers the temperature sensor utilizes the Seebeck effect. Estimates of theoretical performance for a complete megapixel array are quite positive and the prototype single-pixel devices are under test. Superconducting electronics is a critical part of the signal acquisition chain. Three different types of SQUID-array amplifiers coupled to our detector pixels have been tested. The parameters of optimized SQUID-array preamplifiers are discussed.

On the concept of “pumping speed” in gettered and cryopumped systems: T A Giorgi and C Pisani,Vacuum, 16 (12), Dec 1966, 669–675

<dm:abstracts xmlns:dm="http://www.elsevier.com/xml/dm/dtd"><ce:abstract xmlns:ce="http://www.elsevier.com/xml/common/dtd" view="all" class="author" id="aep-abstract-id7"><ce:section-title>Publisher Summary</ce:section-title><ce:abstract-sec view="all" id="aep-abstract-sec-id8"><ce:simple-para id="fsabs008" view="all">This chapter focuses on the current status of HgCdTe molecular-beam epitaxy (MBE) growth technology as practiced in laboratory. The chapter addresses the following topics: a summary of the ‘hardware’ aspects of MBE growth technology, including the role of process sensors, a discussion of the key parameters of the epitaxial growth process and associated thin-film material properties, and a discussion of current state-of-the-art results in device application areas that have been particularly well-served by the evolution of HgCdTe MBE technology. Significant progress has been achieved in HgCdTe MBE growth technology that has enabled the synthesis of complicated multilayer infrared (IR) detector device structures. The development and integration of in situ sensors for monitoring and control of the sensitive HgCdTe MBE growth process, has significantly advanced the capabilities and consistency of the technology, culminating in demonstrations of excellent device performance in a wide variety of IR device architectures such as multispectral detectors, near-IR avalanche photodiodes (APD), high-performance medium wavelength infrared (MWIR) detectors, and megapixel arrays on Silicon (Si) substrates. Cryopumps have found widespread use in MBE systems designed for the growth of HgCdTe alloys. The epitaxial growth of device-quality HgCdTe by MBE is extremely sensitive to fundamental growth parameters such as source fluxes and substrate temperature. MBE growth of HgCdTe generally utilizes Hg, CdTe, and Te as source materials. HgCdTe alloys, because of their unique energy band structure, can be designed to provide low-excess-noise carrier multiplication. MBE growth technology, besides allowing for the integration of sensors that can be used to precisely control the process, also offers the added benefit of excellent lateral uniformity in HgCdTe epitaxial material quality.</ce:simple-para></ce:abstract-sec></ce:abstract></dm:abstracts>