Figure - available from: Journal of Infrared, Millimeter and Terahertz Waves
This content is subject to copyright. Terms and conditions apply.
Thermal runaway of immersed bolometers at extreme bias conditions. Insert shows the optical micrograph of the ruptured sensing element due to bias induced electrical stress
Source publication
Optically immersed bolometer IR detectors were fabricated using electron beam evaporated vanadium oxide as the sensing material. Spin-coated polyimide was used as medium to optically immerse the sensing element to the flat surface of a hemispherical germanium lens. This optical immersion layer also serves as the thermal impedance control layer and...
Citations
... Then, through electrical signal processing, the temperature of the target object is obtained. Nowadays, the main commercial uncooled thermistor materials are amorphous silicon (a-Si), vanadium oxide (VO 2 ), and germanium-siliconoxide [6][7][8]. However, a-Si shows long response times of tens to hundreds of ms [9,10]. ...
Due to their broadband optical absorption ability and fast response times, carbon nanotube (CNT)-based materials are considered promising alternatives to the toxic compounds used in commercial infrared sensors. However, the direct use of pure CNT networks as infrared sensors for simple resistance read-outs results in low sensitivity values. In this work, MoS2 nanoflowers are composited with CNT networks via a facile hydrothermal process to increase the bolometric performance. The thermal diffusivity (α) against temperature (T) is measured using the transient electro-thermal (TET) technique in the range of 320 K to 296 K. The α-T curve demonstrates that the composite containing MoS2 nanoflowers provides significant phonon scattering and affects the intertube interfaces, decreasing the α value by 51%. As the temperature increases from 296 K to 320 K, the relative temperature coefficient of resistance (TCR) increases from 0.04%/K to 0.25%/K. Combined with the enhanced light absorption and strong anisotropic structure, this CNT–MoS2 composite network exhibits a more than 5-fold greater surface temperature increase under the same laser irradiation. It shows up to 18-fold enhancements in resistive responsivity ((Ron − Roff)/Roff) compared with the pure CNT network for a 1550 nm laser at room temperature (RT).
... LEOS has recently embarked upon developing THz detectors that can sense radiations with frequency from 0.1 GHz to 30 THz for space applications 4 . A hybrid detector concept was successfully implemented in which a quasi optical element in the form of a lithographic printed micro dipole antenna was integrated to the V2O5 sensing element at its feed, that was optically immersed on to high resistance float zone (HRFZ) silicon hyper hemispherical lens 5 (Fig. 1). ...
... As for example, the flat surface of a hemispherical germanium lens were used as substrate to deposit vanadium oxide. This type of interfacing is used as sensing material to IR signals of wavelength of 14-16 m [1]. As another example, the highly oriented Ge substrate along the (100), (110) and (111) directions which were used as substrate for the preparation of SrGe 2 were found to be sufficiently good for production of efficient solar cells [2]. ...
This work reports on the modification of electrical properties of amorphous vanadium oxide (a-VOx) thin film thermistor by growth temperature and its effects on the performances of a cooler-free microbolometer. The a-VOx thin films have been deposited by pulsed DC sputtering processes under various growth temperatures from 160 to 230℃. The sheet resistance of the samples at room temperature decreases from 330 to 70 kΩ/▢ with increasing growth temperature. This is due to the increase of oxygen vacancies at higher growth temperature, which have been confirmed by XPS analysis. Temperature dependence of resistance of a-VOx films shows non-hysteresis behaviors up to 120℃, which in turn shows clear activation energies. The activation energy of a-VOx films also decreases from 0.190 to 0.145 eV with increasing growth temperature, which confirms the decrease of temperature coefficient of resistance (TCR) from 2.80 to 2.44 (-%/K) at 25℃ and from 1.48 to 1.14 (-%/K) even at 120℃. The responsivities of fabricated microbolometers based on the a-VOx thin film thermistors have been measured from 3.04 × 10³ to 1.14 × 10³ V/W at room temperature and from 9.54 × 10² to 3.02 × 102 V/W even at 120℃ with increasing growth temperature.
Physics is the interplay of energy and matter. Energy, in the form of light, interacting with matter, principally in the solid state, underpins this topical review. The subject is developed carefully and methodically, beginning with basic definitions pertaining to terahertz detectors and terahertz radiation, then proceeding systematically to delineate characteristics of terahertz photons and terahertz detectors in more detail. In-between, the intimate connection linking terahertz sensors and terahertz sources is highlighted—an important aspect unfortunately often overlooked or ignored when terahertz detectors are discussed in isolation. At the centre of this topical review are the various physical mechanisms by which electromagnetic radiation of terahertz frequencies interacts with matter. The logic is to present first the underlying physical principles of detection before presenting the practical implementation in a specific device, rather than the other way around. A taxonomy of terahertz detectors is then proposed based on the underlying physical principles of detection. Following on from this classification, state-of-the-art terahertz detectors are surveyed and appraised; this overview constitutes the longest section of the review. Key detector parameters which inform applications are then presented and tabulated. Finally, the present state-of-the-art is anchored within the wider scientific context of historical developments and future prospects.
This work uncovers that free-standing partly reduced graphene aerogel (PRGA) films in vacuum exhibit extraordinarily bolometric responses. This high performance is mainly attributed to four structure characteristics: extremely low thermal conductivity (6.0- 0.6 mW·m⁻¹·K⁻¹ from 295 K to 10 K), high porosity, ultralow density (4 mg·cm⁻³), and abundant functional groups (resulting in tunable band gap). Under infrared radiation (peaked at 5.8-9.7 μm), the PRGA film can detect a temperature change of 0.2 K, 1.0 K, and 3.0 K of a target at 3 cm, 25 cm, and 54 cm distance. Even through a quartz window (transmissivity of ~0.98 in the range of 2-4 μm), it can still successfully detect a temperature change of 0.6 K and 5.8 K of a target at 3 cm and 28 cm distance. At room temperature, a laser power as low as 7.5 μW from 405 nm laser and 5.9 μW from 1550 nm laser can be detected. The detecting sensitivity to 1550 nm laser is further increased by 3-fold when the sensor temperature was reduced from 295 K to 12 K. PRGA films are demonstrated to be a promising ultrasensitive bolometric detector, especially at low temperatures.
High performance and reliable infrared detector are ever-sought in spacecraft attitude determination sensor. The most proven “Earth Horizon sensor” based on the infrared detector operating in the wavelength region of 14–16 µm (CO 2 atmospheric emission) essentially calls for IR detector performance; high sensitivity ≥400V/W at low operating bias, fast response ≤ 2 ms, NEP∼200pw/√Hz and long term durability in compliance with space specific conditions. Even though Optically Immersed Bolometer measuring Earth limb radiation budget @14–16µm wavelength region is widely adopted for the Indian Spacecraft ES applications, the sensor reliability was skeptical owing to the inherent disadvantages of materials used and conventional thick film detector technology. Novel fabrication technology for infrared detector has been developed in LEOS to overcome the issue of on-board reliability while achieving better infrared detector performance suitable for same Earth sensor configuration. Detailed design, material studies and characterization were carried out. Fabricated detectors were subjected to environmental tests according to MIL-STD-883F, MIL-STD-810F and MIL-STD-202F as per the Quality Assurance Plan, and their electro optics performance was evaluated. Finally, in house developed and Qualified Bolometer performance has been verified in the spacecraft ES. The paper provides all its details design to application and its specific performance in Earth Horizon Sensor.
