Kun-Tae Kim

Fabrication of vanadium oxide thin film with high-temperature coefficient of resistance using V2O5/V/V2O5 multi-layers for uncooled microbolometers

Vanadium oxide thin film is a promising material for uncooled microbolometers due to its high temperature coefficient of resistance (TCR) at room temperature. It is, however, very difficult to deposit vanadium oxide thin films having a high temperature coefficient of resistance and low resistance because of the process limits in microbolometer fabrication. We present a novel fabrication method for vanadium oxide thin films having good electrical properties. Through the formation of a sandwich structure of V2O5 (100 A)/V (∼80 A)/V2O5 (500 A) by a conventional sputter method and post-annealing at 300 °C in oxygen, a mixed phase of VOx is formed. The results show that the mixed phase formed by this process has a high TCR of more than −2%/°C and low resistivity of <0.1 Ω cm at room temperature.

Enhanced characteristics of an uncooled microbolometer using vanadium–tungsten oxide as a thermometric material

To produce a highly sensitive uncooled microbolometer, the development of a high-performance thermometric material is essential. In this work, amorphous vanadium–tungsten oxide was developed as a thermometric material at a low temperature of 300°C, and the microbolometer, coupled with the material, was designed and fabricated using surface micromachining technology. The vanadium–tungsten oxide showed good properties for application to the microbolometer, such as a high-temperature coefficient of resistance of over −4.0%∕K and good compatibility with the surface micromachining and integrated circuit fabrication process due to its low fabrication temperature. As a result, the uncooled microbolometer could be fabricated with high detectivity over 1.0×109cmHz1∕2∕W at a bias current of 7.5μA and a chopper frequency of 10–20Hz.

Enhanced Characteristics of V0.95W0.05OX-Based Uncooled Microbolometer

In this work, high-performance uncooled microbolometer was fabricated by using vanadium tungsten oxide as a infrared-sensitive material and its bolometric properties was characterized. As a bolometric material, the optimized V_0.95W_0.05O_x thin film has a high TCR value over - 3.0%/K and low noise properties compared with VOx thin film. The fabricated V_0.95W_0.05O_x-based microbolometer was vacuum-packaged and equipped with thermal electric cooler for the measurement of bolometric properties. The TCR value of the fabricated device was -3.49%/K at room temperature resistance of 71 kOmega and the measured thermal conductance was 6.1times10^-7 W/K. Finally, we obtained high responsivity over 1.8times10⁴ W/K and high detectivity over 1.3times10⁹ cmHz^frac12/W at a chopper frequency of 10 Hz and a bias current of 7.4 muA

A floated absorbing structure for uncooled microbolometer

We propose a versatile infrared (IR) absorbing structure for uncooled infrared detectors. We have designed an infrared absorber consisting of five thin film layers (dielectric layer/protection layer/active layer/supporting layer/reflecting layer) that produce a quarter-wavelength resonance condition. It has excellent thermal properties, which are not influenced by the deformation of the thermal isolation structure. We fabricated a microbolometer with the proposed IR absorption structure by a surface micromachining technology. We estimated an IR absorptance of 80%. This IR absorption structure can be applied to both surface micromachining and bulk micromachining.

Fabrication and characterization of a three-dimensional feed-horn infrared antenna for an infrared detector

A three-dimensional feed-horn antenna for the 10-microm-wavelength infrared region has been suggested, characterized, and fabricated. It is applied to an infrared detector for efficient collection of infrared radiation and to reduce background noise. The optimum size of the horn antenna was designed for maximum antenna directivity. The three-dimensional feed-horn antenna mold was fabricated by rotating and tilting illumination, whereas the antenna plate was acquired through electroplating. Antenna characteristics were measured by coupling of the antenna with a microbolometer. Measurement results show that the directivity of the antenna is 16.1 dB and the background noise is reduced by a factor of approximately 2 compared with an open-structure infrared detector.

Enhanced performance of microbolometer using coupled feed horn antenna

In the paper, we improved the performance of the microbolometer using coupled feed horn antenna. The response time of the device was improved by reducing thermal time constant as the area of the absorption layer was reduced. We designed the shape of an absorption layer as circular structure in order to reduce the coupling loss between the antenna and the bolometer. A supporting leg for thermal isolation also has circular structure and its length increased up to 82micrometers , it reduced the thermal conductance to 4.65x 10-8[W/K]. The directivity of the designed antenna has 20.8dB. So the detectivity of the bolometer was improved to 2.37x 10-9 [cm ROOT(Hz)/W] as the noise characteristics of the bolometer was enhanced by coupling feed horn antenna. The fabrication of the bolometer are carried out by a surface micromachining method that uses a polyimide as a sacrificial layer. The absorption layer material of the bolometer is VOx and its TCR value has above 2%/K. The 3-D feed horn antenna structure can be constructed by using a PMER negative photoresist. The antenna and the bolometer can be bonded by Au-Au flip chip bonding method.