Uncooled Thermal Detector Research Articles

Application of Cad Systems to Accounting for Mechanical Stresses in the Development of Uncooled Thermal Detectors of the Bolometric Type

A comparative analysis of the characteristics of the main types of bolometers is indicated in the article. The constructive solution of an uncooled thermal detector of the bolometric type, formed using the technology of microelectromechanical systems, is studied. By means of computer simulation in modern computer-aided design systems in microelectronics, a static mechanical analysis was performed to assess the effect of mechanical stresses arising in structural materials during their formation on the magnitude of deformation. It has been established that to ensure the normal functioning of the microbolometer (to reduce the maximum deviation value of the film from the nominal value), it is necessary to reduce the internal mechanical stresses in the NiCr film. For the Si3N4 films, on the contrary, this value should be increased.

A functional CMOS compatible MEMS pyroelectric detector using 12%-doped scandium aluminum nitride

In this paper, we fabricate and demonstrate a functional complementary metal-oxide-semiconductor (CMOS) compatible pyroelectric uncooled thermal detector using 12% doped Scandium Aluminum Nitride (ScAlN) as the sensing layer. The ScAlN pyroelectric material is deposited at a temperature of ∼200 °C over an 8-in. wafer area. This detector has shown, in general, improved performance compared to AlN, with specific detectivity as high as ∼ 6.08×107 cm Hz/W and noise equivalent power as low as ∼ 8.85×10−10 W/Hz. The results show the specific detectivity of ScAlN-based pyroelectric detectors in the range of 107 cm Hz/W, which is an improvement compared to AlN-based pyroelectric detectors which report specific detectivity typically in the range of 105–106 cm Hz/W. This promising result opens up the opportunities for a CMOS compatible, 8-in. wafer-level manufacturable lead-free pyroelectric detector toward low cost and high throughput, allowing microelectromechanical systems (MEMS) and CMOS integration for increased applications in CMOS–MEMS integrated devices utilizing pyroelectric detectors.

CMOS fully integrated terahertz thermal detector using metamaterial absorber and proportional-to-absolute temperature sensor

Terahertz (THz) detectors have drawn much attention and have been widely applied in imaging, spectroscopy, and sensing fields. An uncooled monolithic resonant THz thermal detector implemented in a standard 55-nm CMOS process is presented. The integration of a frequency selective metamaterial (MM) absorber coupled with an optimized proportional-to-absolute temperature (PTAT) sensor leads to an approach toward uncooled, compact, low-cost, easy-integration, and mass-production THz detectors. The theoretical analysis, design considerations, and characteristic measurements are demonstrated in detail. The proposed thermal detector is designed to resonate at 2.58 THz for the accessible THz source and the natural atmospheric window. The MM absorber achieves near-perfect absorptivity of 98.6%, and the optimized PTAT sensor obtains a high-temperature sensitivity of 10.11 mV / ° C. The calculated responsivity is 49.81 V / W at 2.58 THz with a calculated noise-equivalent power (NEP) of 0.78 μW / Hz0.5 at a modulation frequency of 3 Hz. Relatively better experimental results are obtained at 2.58 THz with a maximum responsivity of 48.3 V / W and a minimum NEP of 1.06 μW / Hz0.5.

Structure Optimized of Uncooled Infrared Sensors

The resistive bolometer based on VOx was studied in the paper. Modeling and simulation was done, and structure was optimized by comparing the different results in thermal and mechanical simulation with different structure and material properties. The improved structures have better thermal response capacity and the mechanical performance, and the absorption efficiency of heat flow has increased by about 18.1%, laid the foundation for the structure amelioration of the uncooled thermal detector.

Modeling of an Uncooled CMOS THz Thermal Detector With Frequency-Selective Dipole Antenna and PTAT Temperature Sensor

A thermal THz detector based on commercial CMOS technology working in room temperature is proposed. The THz electromagnetic wave is first selectively absorbed by an on-chip λ/4 dipole antenna realized in the metallization layer. The absorbed wave energy is then converted to Joule heat energy via a polysilicon resistor. The heat-generated temperature rise is finally detected by a proportional to absolute temperature sensor. The theoretical analysis and physical modeling of the detector including the mechanism of the electromagnetic energy absorption, the thermal conversion, and the electrical circuit response, are presented. The detectors at three typical THz frequencies of 1, 2.9, and 28.3 THz are designed in standard 0.18-μm CMOS technology and post-simulated to illustrate the detector's frequency-selective capability in the whole THz range. The simulated detector's voltage responsivity is 18.0 V/W at 1 THz, 18.9 V/W at 2.9 THz, and 18.6 V/W at 28.3 THz, respectively. The noise equivalent power is 1.7 μW/√Hz at the three frequencies.

Modeling of an uncooled CMOS THz thermal detector with frequency‐selective cross‐dipole antenna and NMOS temperature sensor

AbstractIn this article, we present modeling and simulations of an uncooled thermal THz detector. The detector consists of an on‐chip cross‐dipole antenna, polysilicon resistors, and a temperature sensor. Electromagnetic, thermal, electrical modeling, and simulations of the detector are presented. The three submodels are as follows: THz electromagnetic energy is first selectively absorbed by the antenna realized in the metallization layer. The absorbed wave energy is then converted to Joule heat energy via resistors. Finally, the heat‐generated temperature rise is detected by the temperature sensor. The detectors at three typical THz frequencies of 0.8, 2.9, and 28.3 THz are designed in standard 0.18 μm CMOS technology. Their simulated voltage responsivity is 6.3 V/W at 0.8 THz, 7.2 V/W at 2.9 THz, and 8.2 V/W at 28.3 THz. The noise equivalent power (NEP) is 0.14 μW/√Hz at the three respective frequencies.

Layerwise Monitoring of the Selective Laser Melting Process by Thermography

Abstract Selective Laser Melting is utilized to build parts directly from CAD data. In this study layerwise monitoring of the temperature distribution is used to gather information about the process stability and the resulting part quality. The heat distribution varies with different kinds of parameters including scan vector length, laser power, layer thickness and inter-part distance in the job layout. By integration of an off-axis mounted uncooled thermal detector, the solidification as well as the layer deposition are monitored and evaluated. This enables the identification of hot spots in an early stage during the solidification process and helps to avoid process interrupts. Potential quality indicators are derived from spatially resolved measurement data and are correlated to the resulting part properties. A model of heat dissipation is presented based on the measurement of the material response for varying heat input. Current results show the feasibility of process surveillance by thermography for a limited section of the building platform in a commercial system.

HOT infrared photodetectors

AbstractAt present, uncooled thermal detector focal plane arrays are successfully used in staring thermal imagers. However, the performance of thermal detectors is modest, they suffer from slow response and they are not very useful in applications requiring multispectral detection.Infrared (IR) photon detectors are typically operated at cryogenic temperatures to decrease the noise of the detector arising from various mechanisms associated with the narrow band gap. There are considerable efforts to decrease system cost, size, weight, and power consumption to increase the operating temperature in so-called high-operating-temperature (HOT) detectors. Initial efforts were concentrated on photoconductors and photoelectromagnetic detectors. Next, several ways to achieve HOT detector operation have been elaborated including non-equilibrium detector design with Auger suppression and optical immersion. Recently, a new strategies used to achieve HOT detectors include barrier structures such as nBn, material improvement to lower generation-recombination leakage mechanisms, alternate materials such as superlattices and cascade infrared devices. Another method to reduce detector’s dark current is reducing volume of detector material via a concept of photon trapping detector.In this paper, a number of concepts to improve performance of photon detectors operating at near room temperature are presented. Mostly three types of detector materials are considered — HgCdTe and InAsSb ternary alloys, and type-II InAs/GaSb superlattice. Recently, advanced heterojunction photovoltaic detectors have been developed. Novel HOT detector designs, so called interband cascade infrared detectors, have emerged as competitors of HgCdTe photodetectors.

Applications of pyroelectric materials in array-based detectors

The development of low-cost, uncooled (room temperature operation) thermal detector arrays has been accelerating in recent years and now commercial products are becoming widely available. As costs come down and volumes rise, these devices are entering the consumer marketplace, providing everything from sophisticated security and people-monitoring devices to hand-held thermal imagers for preventative maintenance and building inspection. Two technologies have established significant market shares in uncooled thermal detector array products. These are resistive microbolometers and pyroelectric ceramics. To address the true mass market, the pyroelectric arrays offer significant cost advantage. In this paper, recent developments in a variety of products based on pyroelectric ceramic arrays are described and their performance and applicability are compared and contrasted with competing technologies. This includes the use of low-element-count arrays for applications in people counting and queue measurement, and the drive for cost-effective imaging arrays for mass-market thermal imaging. The technical challenges in materials production, device development, and low-cost manufacture are reviewed and future opportunities and challenges are outlined.

Theoretical comparison of thermal contrast detected with thermal and quantum detector

We perform the theoretical comparison between the detected thermal contrast measured with a quantum and uncooled thermal detector. For earth based remote monitoring of room temperature processes, the detection of contrast using the quantum detector is by a factor of about 20 better than with the thermal one, even in the case that the detected thermal contrast arises solely due to changes in emissivity. Consequently, minute emissivity changes arising due to disease onset can be monitored by an appropriately selected detector and the wavelength interval of its operation. This is applicable equally to crop monitoring and to the non-invasive detection of sub-surface cancer in humans.

Uncooled long wavelength infrared photon detectors

Infrared (IR) photon detectors operating in the middle (3–5 μm) and long wavelength (8–14 μm) infrared spectral range require cryogenic cooling to achieve useful performance. The need for cooling is a major limitation of IR photon detectors what prevents more widespread use of IR technology. At present, uncooled thermal detector focal plane arrays are successfully used in staring thermal imagers. However, the performance of thermal detectors is modest, they suffer from slow response and they are not very useful in applications requiring multispectral detection. In the paper, a number of concepts to improve performance of photon detectors operating at room temperature are presented. Several types of detector materials are considered: HgCdTe, Sb-based III–V ternary alloys, and type-II InAs/GaInSb superlattice. Initial efforts were concentrated on photoconductors and photoelectromagnetic detectors. Recently, advanced heterojunction photovoltaic detectors have been developed. It is shown that uncooled HgCdTe photovoltaic detector can achieve detectivity of 10 9 cm Hz 1/2 W −1 at the 8–9 μm range. Potentially the devices can be assembled in large focal plane arrays. This will enable obtaining of NEDT of less than 0.1 K for staring thermal imagers operating with f/1 optics and 30 s −1 frame rate.