Design of a Readout Integrated Circuit (ROIC) for Infrared Imaging Applications

There has been a growing interest in using Infrared (IR) imaging systems in various applications ranging from medical diagnosis to military surveillance. The quality of the IR imaging systems depends on 1) the sensitivity of the Focal Plane Arrays (FPA) as the transducer of the electromagnetic wave and 2) the Readout Integrated Circuit (ROIC) that provides the pixel data to the processing unit. In this thesis, we describe specific ROIC designed for a dual-band IR imaging system. In particular, we focus on the ROIC part and propose an efficient circuit that meets several design objectives, including minimum power, minimum cost, and maximum dynamic range. We start with analog design of different parts of the circuit based upon a bottom-up design discipline. We then validate our design using TSpice simulation and analyzing the time/frequency response of the circuit at each step. Next, we proceed with layout design, where we present our final ROIC layout designed using Tanner EDA tools. Finally, we explain the ROIC test bed developed at the Center for High Technology Materials (CHTM), University of New Mexico, which can be used to test Indigo-based IR imaging systems as well as our designed ROIC

Longwave and bi-color type-II InAs/(In)GaSb superlattice infrared detectors

Infrared (IR) photodetectors are useful for a variety of military and civil applications such as target acquisition, medical diagnostics, pollution monitoring, to name just a few. Presently photonic IR detectors are based on interband transitions in low bandgap semiconductors such as mercury cadmium telluride (MCT) or InSb or in intersubband transitions in hetero-engineered structures such as quantum well or quantum dot infrared photodetectors (QWIPs or QDIPs). These detectors operate at low temperatures (77 K-200 K) in order to obtain high signal to noise ratio. The cooling requirement limits the lifetime, increases the weight and the total cost, as well as the power budget, of the whole infrared system. There is a concerted effort to develop photonic detectors operating at higher temperatures. In the past few years, interband transitions in type II InAs/GaSb strain layer superlattices (SL)have emerged as a competing technology among other IR systems. Although MCT and QWIP technologies are relatively more mature than the SL technology, the SL technology has potential to enhance performance in several key areas. One of the main advantages of this system lies in the fact that the effective band gap of the SL can be tailored over a wide range (3 μm \u3c λc \u3c 30 μm) by varying the thickness of two mid bandgap\u27 constituent materials, namely GaSb and InAs. Tunneling currents in SL are reduced due to a larger electron effective mass. Large splitting between heavy-hole and light-hole valence subbands due to strain in the SLs contributes to the suppression of Auger recombination. Moreover, the band structure of the SL can be engineered to enhance carrier lifetimes and reduce noise at higher temperatures. SL based IR detectors have demonstrated high quantum efficiency, high temperature operation, and are suitable for incorporation in focal plane arrays (FPA) by tapping into the mature III-V based growth and fabrication processes. The recently proposed nBn heterostructure design has demonstrated a 100 K increase in background-limited infrared photodetection (BLIP) for InAs-based device, by decreasing Shockley-Read-Hall generation currents and by suppressing surface currents using specific processing. Third generation IR detectors have three main emphases, high operating temperature (HOT), multicolor capability, and large format arrays. This work concentrates on multicolor and HOT IR detectors based on nBn design. Contributions of this thesis include 1. Development of design and growth procedure for the long-wave (LW) SL detectors leading to an improved detector performance: 13 MLs of InAs and 7 MLs of GaSb with InSb strain compensating layer were designed and optimized for LW SL detectors. LWIR pin and nBn detectors were introduced and their optical and electrical properties were compared. LW nBn detectors show higher device performance in terms of lower dark current density and higher responsivity as compared to the LW pin detectors. The reduction in dark current in LW nBn detector is due to reduction of SRH centers as well as surface leakage currents. The increase in responsivity for LW nBn detectors is due to reduction non-radiative SRH recombination. 2. Design, growth and characterization of bi-color nBn detectors: Present day two color SL detectors require two contacts per pixel leading to a complicated processing scheme and expensive read out integrated circuits (ROICs). The nBn architecture was modified to realize a dual-band response by changing the polarity of applied bias using single contact processing. The spectral response shows a significant change in the LWIR to MWIR ratio within a very small bias range ( 3c100 mV ) making it compatible with commercially available ROICs. 3. Investigation of background carrier concentration in SLs: The electrical transport in SLs was investigated in order to improve the collection efficiency and understand SL devices performance operating at ambient temperature. For this purpose background carrier concentration of type-II InAs/GaSb SLs on GaAs substrates are studied. The hall measurements on mid-wave SLs revealed that the conduction in the MWIR SLs is dominated by holes at low temperatures (\u3c 200 K) and by electrons at high temperatures (\u3e 200 K) and is dominated by electrons at all temperatures for LWIR SLs possibly due to the thicker InAs (residually n-type) and thinner GaSb (residually p-type) layers. By studying the in-plane transport characteristics of LW SLs grown at different temperatures, it was shown that interface roughness scattering is the dominant scattering mechanism at higher temperatures (200 K- 300 K).\u2

(Commit-and-Prove) Predictable Arguments with Privacy

Predictable arguments introduced by Faonio, Nielsen and Venturi (PKC17) are private-coin argument systems where the answer of the prover can be predicted in advance by the verifier. In this work, we study predictable arguments with additional privacy properties. While the authors in [PKC17] showed compilers for transforming PAs into PAs with zero-knowledge property, they left the construction of witness indistinguishable predictable arguments (WI-PA) in the plain model as an open problem. In this work, we first propose more efficient constructions of zero-knowledge predictable arguments (ZK-PA) based on trapdoor smooth projective hash functions (TSPHFs). Next, we consider the problem of WI-PA construction in the plain model and show how to transform PA into WI-PA using non-interactive witness-indistinguishable proofs. As a relaxation of predictable arguments, we additionally put forth a new notion of predictability called Commit-and-Prove Predictable Argument (CPPA), where except the first (reusable) message of the prover, all the prover’s responses can be predicted. We construct an efficient zero-knowledge CPPA in the non-programmable random oracle model for the class of all polynomial-size circuits. Finally, following the connection between predictable arguments and witness encryption, we show an application of CPPAs with privacy properties to the design of witness encryption schemes, where in addition to standard properties, we also require some level of privacy for the decryptors who own a valid witness for the statement used during the encryption process

Growth and characteristics of type-II InAs/GaSb superlattice-based detectors

We report on growth and device performance of infrared photodetectors based on type II InAs/Ga(In)Sb strain layer superlattices (SLs) using the complementary barrier infrared detector (CBIRD) design. The unipolar barriers on either side of the absorber in the CBIRD design in combination with the type-II InAs/GaSb superlattice material system are expected to outperform traditional III-V LWIR imaging technologies and offer significant advantages over the conventional II-VI material based FPAs. The innovative design of CBIRDS, low defect density material growth, and robust fabrication processes have resulted in the development of high performance long wave infrared (LWIR) focal plane arrays at JPL

Analysis of affecting factors on patient safety culture in public and private hospitals in Iran

Background: Patient safety culture is one of the main components of the quality of health services and is one of the main priorities of health studies. Accordingly, this study aimed to determine and compare the views of healthcare staff on the patient safety culture and the impact of effective factors on patient safety culture in public and private hospitals in Tehran, Iran. Methods: This cross-sectional study was carried out on a sample of 1203 health care workers employed in three public and three private hospitals in Tehran, Iran. Stratified random sampling was used in this study. Data were collected using the Maslach burnout inventory and patient safety culture questionnaire (HSOPSC). IBM SPSS v22 and Amos v23 were used to perform path analysis. Results: Eight hundred sixty-seven (72.57%) females and 747 (27.43%) males with a mean age of 33.88 +/- 7.66 were included. The average percentage of positive responses to the safety culture questionnaire in public and private hospitals was 65.5 and 58.3%, respectively. The strengths of patient safety culture in public hospitals were in three dimensions including non-punitive response to errors (80%), organizational learning-continuous improvement (79.77%), and overall perceptions of patient safety (75.16%), and in private hospitals, were three dimensions including non-punitive responses to errors (71.41%), organizational learning & continuous improvement (69.24%), and teamwork within units (62.35%). The type of hospital and work-shift hours influenced the burnout and patient safety questionnaire scores (P-value < 0.05). The path analysis results indicate the fitness of the proposed model (RMSEA = 0.024). The results showed a negative impact of a work shift (beta = - 0.791), occupational burnout (beta = - 0.554) and hospital type (beta = - 0.147) on the observance of patient safety culture. Conclusion: Providing feedback on errors and requirements for the frequent incident reporting, and patient information exchange seem necessary to promote the patient safety culture. Also, considering the negative impact of the shift work and burnout on patient safety culture, by planning and managing these factors appropriately, correct actions could be designed to improve the safety culture. Keywords:Patient safety culture; Shift work; Job burnout; Path analysi

Unipolar Barrier Dual-Band Infrared Detectors

Dual-band barrier infrared detectors having structures configured to reduce spectral crosstalk between spectral bands and/or enhance quantum efficiency, and methods of their manufacture are provided. In particular, dual-band device structures are provided for constructing high-performance barrier infrared detectors having reduced crosstalk and/or enhance quantum efficiency using novel multi-segmented absorber regions. The novel absorber regions may comprise both p-type and n-type absorber sections. Utilizing such multi-segmented absorbers it is possible to construct any suitable barrier infrared detector having reduced crosstalk, including npBPN, nBPN, pBPN, npBN, npBP, pBN and nBP structures. The pBPN and pBN detector structures have high quantum efficiency and suppresses dark current, but has a smaller etch depth than conventional detectors and does not require a thick bottom contact layer

Barrier infrared detector

A superlattice-based infrared absorber and the matching electron-blocking and hole-blocking unipolar barriers, absorbers and barriers with graded band gaps, high-performance infrared detectors, and methods of manufacturing such devices are provided herein. The infrared absorber material is made from a superlattice (periodic structure) where each period consists of two or more layers of InAs, InSb, InSbAs, or InGaAs. The layer widths and alloy compositions are chosen to yield the desired energy band gap, absorption strength, and strain balance for the particular application. Furthermore, the periodicity of the superlattice can be "chirped" (varied) to create a material with a graded or varying energy band gap. The superlattice based barrier infrared detectors described and demonstrated herein have spectral ranges covering the entire 3-5 micron atmospheric transmission window, excellent dark current characteristics operating at least 150K, high yield, and have the potential for high-operability, high-uniformity focal plane arrays

Single-Band and Dual-Band Infrared Detectors

Bias-switchable dual-band infrared detectors and methods of manufacturing such detectors are provided. The infrared detectors are based on a back-to-back heterojunction diode design, where the detector structure consists of, sequentially, a top contact layer, a unipolar hole barrier layer, an absorber layer, a unipolar electron barrier, a second absorber, a second unipolar hole barrier, and a bottom contact layer. In addition, by substantially reducing the width of one of the absorber layers, a single-band infrared detector can also be formed