Design and Fabrication of Vertically-Integrated CMOS Image Sensors

Technologies to fabricate integrated circuits (IC) with 3D structures are an emerging trend in IC design. They are based on vertical stacking of active components to form heterogeneous microsystems. Electronic image sensors will benefit from these technologies because they allow increased pixel-level data processing and device optimization. This paper covers general principles in the design of vertically-integrated (VI) CMOS image sensors that are fabricated by flip-chip bonding. These sensors are composed of a CMOS die and a photodetector die. As a specific example, the paper presents a VI-CMOS image sensor that was designed at the University of Alberta, and fabricated with the help of CMC Microsystems and Micralyne Inc. To realize prototypes, CMOS dies with logarithmic active pixels were prepared in a commercial process, and photodetector dies with metal-semiconductor-metal devices were prepared in a custom process using hydrogenated amorphous silicon. The paper also describes a digital camera that was developed to test the prototype. In this camera, scenes captured by the image sensor are read using an FPGA board, and sent in real time to a PC over USB for data processing and display. Experimental results show that the VI-CMOS prototype has a higher dynamic range and a lower dark limit than conventional electronic image sensors

Self-powered GHZ solution-processed hybrid perovskite photodetectors

Organic-inorganic hybrid perovskite (OIHP) based photo-responsive devices include an OIHP active layer disposed between a cathode layer and an anode layer, and an electron extraction layer disposed between the cathode layer and the active layer. The electron extraction layer includes a layer of C60 directly disposed on the active layer. The active layer includes an organometal trihalide perovskite layer (e.g., CH3NH3PbI2X, where X includes at least one of Cl, Br, or I)

Infrared Photodetectors based on Nanowire Arrays with Embedded Quantum Heterostructures

Optical sensors operating in the infrared range of the electromagnetic spectrum are key components in a variety ofapplications including optical communication, night vision, medical diagnosis, surveillance, and astronomy.Semiconductor nanowires have great potential for realizing broadband infrared photodetectors with excellentresponsivity, low dark current and low noise, and a unique compatibility with commercial silicon-based electronics.In this thesis work, comprising three published articles in Nano Letters, we synthesized, characterized andmodeled disruptive infrared photodetectors based on InP nanowires with axially embedded InAsP quantum discs.In the first article, we made a combined study of design, growth, device processing and optoelectronic propertiesof n+−i−n+ InP detector elements comprising 4 million periodically ordered nanowires in arrays, including either asingle or 20 InAsP quantum discs. Optimized Zn compensation of the residual non-intentional n-dopants in the isegmentsuppressed the dark current at room-temperature to a few pA/NW. The detector elements exhibit astrong broadband photoresponse with contributions from both the InP and InAsP segments with a thresholdwavelength of about 2.0 μm and a bias-tunable responsivity reaching 7 A/W@ 1.38 μm at 2 V bias.In the second article, we performed an in-depth experimental and theoretical investigation of the responsivity ofoptimized photodetectors under different illumination conditions. The photodetectors exhibit strongly bias andpower-dependent responsivities reaching record-high values of 250 A/W at 980 nm/20 nW and 990 A/W at 532nm/60 nW, both at 3.5 V bias. Complementary real device modeling revealed a new photogating mechanism,induced by the complex charge carrier dynamics involving optical excitation and recombination in the quantumdiscs and interface traps, which reduces the electron transport barrier between the n+ segment and the i-segmentunder illumination.Finally, in the last article, we demonstrate the first intersubband photocurrent response in a nanowireheterostructure array photodetector. The infrared response from 3 to 20 μm is enabled by intersubband transitionsin the low-bandgap InAsP quantum discs. The intriguing optical characteristics, including unexpected sensitivity tonormal incident radiation, are partly explained by excitation of the longitudinal component of optical modes in thephotonic crystal formed by the nanostructured portion of the detectors.Our results show that properly designed arrays of axial nanowire heterostructures are promising candidates forrealization of commercially viable broadband photodetectors

High-Temperature Optoelectronic Device Characterization and Integration Towards Optical Isolation for High-Density Power Modules

Power modules based on wide bandgap (WBG) materials enhance reliability and considerably reduce cooling requirements that lead to a significant reduction in total system cost and weight. Although these innovative properties lead power modules to higher power density, some concerns still need to be addressed to take full advantage of WBG-based modules. For example, the use of bulky transformers as a galvanic isolation system to float the high voltage gate driver limits further size reduction of the high-temperature power modules. Bulky transformers can be replaced by integrating high-temperature optocouplers to scale down power modules further and achieve disrupting performance in terms of thermal management, power efficiency, power density, operating environments, and reliability. However, regular semiconductor optoelectronic materials and devices have significant difficulty functioning in high-temperature environments. Modular integration of optoelectronic devices into high-temperature power modules is restricted due to the significant optical efficiency drop at elevated temperatures. The quantum efficiency and long-term reliability of optoelectronic devices decrease at elevated temperatures. The motivation for this study is to develop optoelectronic devices, specifically optocouplers, that can be integrated into high-density power modules. A detailed study on optoelectronic devices at high temperature enables us to explore the possibility of scaling high-density power modules by integrating high-temperature optoelectronic devices into the power module. The primary goal of this study is to characterize and verify the high-temperature operation of optoelectronic devices, including light-emitting diodes and photodiodes based on WBG materials. The secondary goal is to identify and integrate optoelectronic devices to achieve galvanic isolation in high-density power modules working at elevated temperatures. As part of the study, a high-temperature packaging, based on low temperature co-fired ceramic (LTCC), suitable to accommodate optoelectronic devices, will also be designed and developed

Nano-grating assisted light absorption enhancement for msm-pds performance improvement: An updated review

The primary focus of this review article mainly emphasizes the light absorption enhancement for various nanostructured gratings assisted metal-semiconductor-metal photodetectors (MSM-PDs) that are so far proposed and developed for the improvement of light capturing performance. The MSM-PDs are considered as one of the key elements in the optical and high-speed communication systems for applications such as faster optical fiber communication systems, sensor networks, high-speed chip-to-chip interconnects, and high-speed sampling. The light absorption enhancement makes the MSM-PDs an ideal candidate due to their excellent performances in detection, especially in satisfying the high-speed or high-performance device requirements. The nano-grating assisted MSM-PDs are preordained to be decorous for many emerging and existing communication device applications. There have been a significant number of research works conducted on the implementa-tion of nano-gratings, and still, more researches are ongoing to raise the performance of MSM-PDs particularly, in terms of enhancing the light absorption potentialities. This review article aims to provide the latest update on the exertion of nano-grating structures suitable for further developments in the light absorption enhancement of the MSM-PDs

Terahertz and mid-infrared photodetectors based on intersubband transitions in novel materials systems

The terahertz (THz) and mid-infrared (MIR) spectral regions have many potential applications in the industrial, biomedical, and military sectors. Yet, a wide portion of this region of the electromagnetic spectrum (particularly the THz range) is still relatively unexplored, due mainly to the absence of suitable sources and photodetectors, related to the lack of practical semiconductor materials with adequately small band gap energies. Intersubband transitions (ISBTs) between quantized energy states in quantum heterostructures provide tunable wavelengths over a broad spectral range including the THz region, by choosing appropriate layer thicknesses and compositions. This work focuses on the development of THz and MIR Quantum Well Infrared Photodetectors (QWIPs) based on ISBTs in GaN/AlGaN and Si/SiGe heterostructures. Due to their large optical phonon energies, GaN materials allow extending the spectral reach of existing far-infrared photodetectors based on GaAs, and may enable higher-temperature operation. In the area of MIR optoelectronic devices, I have focused on developing QWIPs based on ISBTs in Si/SiGe heterostructures in the form of on strain-engineered nanomembranes. Due to their non-polar nature, these materials are free from reststrahlen absorption and ultrafast resonant electron/phonon scattering, unlike traditional III-V semiconductors. Therefore, Si/SiGe quantum wells (QWs) are also promising candidates for high-temperature high-performance ISB device operation (particularly in the THz region), with the additional advantage of direct integration with CMOS technology. In this thesis work, numerical modeling is used to design the active region of the proposed devices, followed by sample fabrication and characterization based on lock-in step-scan Fourier transform infrared spectroscopy. Three specific QWIP devices have been developed. The first is a III-nitride THz QWIP based on a novel double-step QW design in order to alleviate the material limitations provided by the intrinsic electric fields of GaN/AlGaN heterostructures. Next, I have developed a THz GaN/AlGaN QWIP grown on semi-polar (202 ̅1 ̅) GaN, where the detrimental effects of the internal fields are almost completely eliminated. Finally, I have demonstrated a Si/SiGe MIR QWIP based on a novel fabrication approach, where nanomembrane strain engineering is used to address the materials quality issues normally found in SiGe QWs. Promising photodetector performance is obtained in all cases.2017-06-21T00:00:00

Enhanced Light Absorption and Electro-absorption Modulation Based on Graphene and Conductive Oxide

The development of integrated photonics is limited by bulky and inefficient photonic component compared to their electronic counterparts due to weak light-matter interactions. As the key devices that determine the performance of integrated photonic circuits, electro-optical (EO) modulators are inherently built on the basis of enhancing light-matter interactions. Current EO modulators often deploy conventional materials with poor EO properties, or ring resonator structure with narrow bandwidth and thermal instability, so their dimensions and performance have nearly reached their physical limits. Future integrated photonic interconnects require EO modulators to be ultra-compact, ultra-fast, cost-effective and able to work over a broad bandwidth. The key to achieving this goal is to identify an efficient and low-cost active material. Meanwhile, novel waveguides and platforms need to be explored to significantly enhance light-active medium interaction. As widely investigated novel materials, graphene and conductive oxide (COx) have shown remarkable EO properties. The objective of this dissertation is to realize enhanced light-matter interaction based on these two novel materials and waveguiding platforms, and further develop ultra-compact, ultra-fast EO modulators for future photonic integrated circuits. The first part of this dissertation covers the theory of EO modulation mechanisms, several types of EO materials including graphene and COx, as well as fabrication techniques. The second part demonstrates greatly enhanced light absorption based on mono-/multi-layer graphene. The third part proposes the theoretical study of nanoscale EA modulators based on ENZ-slot waveguide. The fourth part explores the field effect within a MOS-like structure, and verifies the ENZ behavior of COx. The fifth part experimentally demonstrates both plasmonic and dielectric configurations for ultra-compact and ultra-fast EA modulators. The final part summarizes the work presented in this dissertation and also discusses some future work for photonic applications