Vanadium Oxide Microbolometers with Patterned Gold Black or Plasmonic Resonant Absorbers

High sensitivity uncooled microbolometers are necessary to meet the needs of the next generation of infrared detectors, which seek low power consumption and production cost without sacrificing performance. Presented here is the design, fabrication, and characterization of a microbolometer with responsivity enhanced by novel highly absorptive coatings. The device utilizes a gold-doped vanadium oxide film in a standard air bridge design. Performance estimations are calculated from current theory, and efforts to maximize signal to noise ratio are shown and evaluated. Most notably, presented are the experimental results and analysis from the integration of two different absorptive coatings: a patterned gold black film and a plasmonic resonant structure. Infrared-absorbing gold black was selectively patterned onto the active surfaces of the detector. Patterning by metal lift-off relies on protection of the fragile gold black with an evaporated oxide, which preserves gold black\u27s near unity absorptance. This patterned gold black also survives the dry-etch removal of the sacrificial polyimide used to fabricate the air-bridge bolometers. Infrared responsivity is improved 70% for mid-wave IR and 22% for long-wave IR. The increase in the thermal time constant caused by the additional mass of gold black is a modest 15%. However, this film is sensitive to thermal processing; experimental results indicate a decrease in absorptance upon device heating. Sub-wavelength resonant structures designed for long-wave infrared (LWIR) absorption have also been investigated. Dispersion of the dielectric refractive index provides for multiple overlapping resonances that span the 8-12 ?m LWIR wavelength band, a broader range than can be achieved using the usual resonance quarter-wave cavity engineered into the air-bridge structures. Experimental measurements show an increase in responsivity of 96% for mid-wave IR and 48% for long-wave IR, while thermal response time only increases by 16% due to the increased heat capacity. The resonant structures are not as susceptible to thermal processing as are the gold black films. This work suggests that plasmonic resonant structures can be an ideal method to improve detector performance for microbolometers

Analysis and comparison of resistive, ferroelectric and pyroelectric uncooled bolometers for electronic imaging systems

The performance parameters (responsivity (Rv). detectivity (D*), total noise and response time) of resistive, pyroelectric and ferroelectric bolometer detectors are dependent on a large number of key variables including chopping frequercy, the input impedance and voltage noise of the readout circuitry, the structure dependent parameters (particularly thermal conductance and thermal capacitance), and material properties such as dielectric constant, pyroelectric coefficient, loss tangent and thin film thickness. The interrelationship between the key variables and their influence on performance is often complex and not easily discerned for the three major types of thermal detectors: resistive, pyroelectric and ferroelectric bolometers. In this thesis research, the dependence of Rv, D* and total noise on these key parameters were analyzed and written as equations from which computer calculations could easily be made. The analyzed results were used to compare the pertbrmance of the three types of sensors for present-day structure and material characteristics and also for material characteristics and structures that night be developed in the future

Silicon based uncooled microbolometer

During the last decade, uncooled microbolometer infrared detectors have attracted the attention of military and civilian infrared detection and imaging industry due to their significant advantages. In actuality, infrared imaging systems play a critical role in sectors such as thermography (predictive maintenance and building inspection), commercial and civilian applications (vision automotive, surveillance, navigation and fire-fighting), and defense industry (thermal weapon sight, soldier vision and vehicle vision enhancer). Compared with the cryogenically cooled infrared photon detectors, uncooled infrared imaging technology offers advantages such as operation at room temperature, light weight and size, reduced power consumption, easy integration with read-out electronics and broadband response capability. The motivation for this study is the consideration of silicon as an alternative candidate to replace the standard infrared detector thermosensing materials, as a result of its low cost and easy integration with the actual silicon planar lithography microfabrication techniques. No prior attempts are known in the literature on the use of low doped p-type silicon (p-Si) as a thermosensing material in thermal infrared detectors. The main aim of this research work is the design, modeling and simulation of low doped p-Si based uncooled microbolometer infrared detector. The theoretical optical modeling, and electronic performance are analyzed and explained. Radiative properties, as function of thin film thickness, of some commonly used thin films of dielectric materials, aluminum oxide (Al2O3), silicon dioxide (SiO2), aluminum nitride (AlN) and silicon nitride (Si3N4) are investigated within the infrared spectral range of 1.5-14.2 μm. A novel thermally isolated, suspended square-shaped multilayer structure microbolometer is proposed. Its radiative properties are simulated and optimized in the long wavelength spectral range of 8-14 µm (transmission window at room temperature). The performance of the proposed microbolometer structure is numerically calculated by the figures of merit that characterize the thermal detector response. The dimensions of the microbolometer structure are optimized in order to achieve the maximum responsivity and low thermal time response required by the imaging systems, while securing the stability and support of the structure

Miniaturized Silicon Photodetectors

Silicon (Si) technologies provide an excellent platform for the design of microsystems where photonic and microelectronic functionalities are monolithically integrated on the same substrate. In recent years, a variety of passive and active Si photonic devices have been developed, and among them, photodetectors have attracted particular interest from the scientific community. Si photodiodes are typically designed to operate at visible wavelengths, but, unfortunately, their employment in the infrared (IR) range is limited due to the neglectable Si absorption over 1100 nm, even though the use of germanium (Ge) grown on Si has historically allowed operations to be extended up to 1550 nm. In recent years, significant progress has been achieved both by improving the performance of Si-based photodetectors in the visible range and by extending their operation to infrared wavelengths. Near-infrared (NIR) SiGe photodetectors have been demonstrated to have a “zero change” CMOS process flow, while the investigation of new effects and structures has shown that an all-Si approach could be a viable option to construct devices comparable with Ge technology. In addition, the capability to integrate new emerging 2D and 3D materials with Si, together with the capability of manufacturing devices at the nanometric scale, has led to the development of new device families with unexpected performance. Accordingly, this Special Issue of Micromachines seeks to showcase research papers, short communications, and review articles that show the most recent advances in the field of silicon photodetectors and their respective applications

Fabrication of vanadium oxide for uncooled FPAs using dual magnetron AC sputtering

Conference Name:2011 International Conference on Electronic and Mechanical Engineering and Information Technology, EMEIT 2011. Conference Address: Harbin, China. Time:August 12, 2011 - August 14, 2011.This paper presents a novel equipment with an improved structure of the magnetron sputtering for thin film fabrication. By using this equipment, a vanadium oxide thin film with a better TCR and uniformity can be fabricated. In this equipment, two magnets are aligned with the wafer table eccentrically so that the coupling effect is rendered. This changes the distribution of magnetic field lines for each single sputtering target; as a result, a magnetic field gradient in the z-directionis generated, which acts on Ar together with the alternating current (AC) electric field. Consequently, the goal of using relatively small sputtering target material to generate large uniform film on the substrate is achieved. Besides, there being no sedimentary insulation on the anode as the traditional structure, it can avoid the periodical purification for the equipment to ensure the continuous work. ? 2011 IEEE

CONCEPTUAL DESIGN REPORT

Brookhaven National Laboratory has prepared a conceptual design for a world class user facility for scientific research using synchrotron radiation. This facility, called the ''National Synchrotron Light Source II'' (NSLS-II), will provide ultra high brightness and flux and exceptional beam stability. It will also provide advanced insertion devices, optics, detectors, and robotics, and a suite of scientific instruments designed to maximize the scientific output of the facility. Together these will enable the study of material properties and functions with a spatial resolution of {approx}1 nm, an energy resolution of {approx}0.1 meV, and the ultra high sensitivity required to perform spectroscopy on a single atom. The overall objective of the NSLS-II project is to deliver a research facility to advance fundamental science and have the capability to characterize and understand physical properties at the nanoscale, the processes by which nanomaterials can be manipulated and assembled into more complex hierarchical structures, and the new phenomena resulting from such assemblages. It will also be a user facility made available to researchers engaged in a broad spectrum of disciplines from universities, industries, and other laboratories