Xinjian Yi

Nanostructured vanadium dioxide thin films with low phase transition temperature

A low phase turning temperature of 35°C has been observed in the semiconductor-to-metal transition of nanoscale vanadium dioxide (VO2) thin films. The thin films are prepared by reactive ion beam sputtering deposition and subsequent thermal annealing. Both scanning electron microscopy and transmission electron microscopy measurements show that the grain size of the fabricated VO2 thin films are several tens of nanometers. The average height of the crystallite is 20nm and the grain diameter is between 20 and 100nm. The low-temperature phase transition is accompanied by a significant change in the thin film’s infrared transmission property.

Characterization of nanostructured VO 2 thin films grown by magnetron controlled sputtering deposition and post annealing method

By magnetron controlled sputtering system, a new nanostructured metastable monoclinic phase VO2 (B) thin film has been fabricated. The testing result shows that this nanostructured VO2 (B) thin film has high temperature coefficient of resistance (TCR) of -7%/K. Scanning electron microscopy measurement shows that the average grain diameter of the VO2 (B) crystallite is between 100 and 250 nm. After post annealed, VO2 (B) crystallite is changed into monoclinic (M) phase VO2 (M) crystallite with the average grain diameter between 20 and 50 nm. A set up of testing the thin film switching time is established. The test result shows the switching time is about 50 ms. With the nanostructured VO2 (B) and VO2 (M) thin films, optical switches and high sensitivity detectors will be presented.

Micromachined Uncooled IR Bolometer Linear Array Using VO2 Thin Films

Mixed vanadium oxide thin films, as VO2 for the main composition are materials for uncooled microbolometer due to their high temperature coefficient of resistance (TCR) at room temperature. This paper describes the design and fabrication of 8-element linear array IR uncooled microbolometers using the films and micromachining technology. The characteristics of the array is investigated in the spectral region of 8–12 μm. The fabricated detectors exhibit responsivity of up to 10 KV/W, typical detectivity of 1.89×108 cmHz1/2/W, and thermal time constant of 11 ms, at 296 K and at a frequency of 30 Hz. Furthermore, The uncorrected response uniformity of the linear array bolometers is less than 20%.

Monolithic integration technique for microlens arrays with infrared focal plane arrays

Abstract Based on scalar diffraction theory, 8-phase-level 256×290 element diffractive microlens arrays with lenslet dimension of 50×33 μm 2 have been fabricated on the back side of PtSi infrared focal plane arrays. The design and fabrication process are discussed. The measurement results indicate that the imaging quality has been greatly improved and the ratio of the signal-to-noise of the infrared focal plane array integration with microlens array is increased by a factor of 2.5.

Responsivity calculation and measurement of YBaCuO optical detector

The optical response of granular YBa/sub 2/Cu/sub 3/O/sub 7- delta / films using microbridge structure was investigated. Considering the self-heating effect of the detector from the bias current, a bolometric model was proposed to calculate the temperature rise and responsivity of the bolometer. The responsivity of a nonequilibrium detector on the basis of grain boundary Josephson junctions in granular films has also been demonstrated. Optical detectors with responsivities of more than 10/sup 3/ v/w at liquid nitrogen temperature have been fabricated. Experimental evidence for the coexistence of bolometric and nonbolometric effect is given. Calculations based on the proposed model are in agreement with the experimental results.<<ETX>>

A novel method of fabrication of microlens arrays

Abstract A new self-alignment process to fabricate microlens arrays is introduced. By this method, during the fabrication process, the rigorous alignment is avoided which has great effect on diffraction efficiency in the conventional multi-photolithography process. The large arrays of 1500×640 element silica microlens are manufactured by this method. The measurement results show that the eight-phase-level microlens arrays diffraction efficiency is as high as 93%.

Design and optical performance research of multi-phase diffractive microlens arrays

To improve the performance of infrared focal plane arrays, multi-phase-level 256 × 256 element diffractive microlens arrays with a center wavelength of 4 µm are designed using a novel partial etching method based on the scalar diffraction theory and computer aided design. A testing system is established with an optical communication semiconductor laser and detector for measuring the diffraction efficiency and point spread function of the designed multi-phase diffractive microlens arrays. The measurement results indicate that the measured diffraction efficiency of 16-phase Si and quartz diffractive microlens arrays are 83.7% and 87.5%, respectively, and the optical response of the infrared focal plane arrays with integration of the diffractive microlens arrays is increased by a factor of 2.23.

VO2-Based Infrared Microbolometer Array

V02-based thin film materials on silicon substrates are fabricated by ion beam sputtering and a post-annealing which is different from the conventional fabricating method. An infrared linear microbolometer array with 128 pixels is prepared using as-deposited vanadium dioxide thin films. Optical and electrical properties for V02-based microbolometer array are tested.

VO 2-based microbolometer uncooled infrared focal plane arrays with CMOS readout integrated circuit

Thin films of vanadium dioxide (VO2) were selected for microbolometers. The thin films were fabricated with a novel method mainly including ion-sputtering and annealing. It is found that the electrical properties of these thin films can be controlled by adjusting the time of ion-sputtering and annealing. A standard microbolometer pixel structure of micro-bridge has been applied. Two-dimensional arrays of microbolometers have been fabricated on silicon integrated circuit wafers using a surface micromachining technique. A new type of on-chip readout integrated circuit (ROIC) for 32×32 pixel bolometric detector arrays has been designed and fabricated using a 1.5μm double metal poly complementary metal oxide semiconductor (CMOS) processing. The readout circuit consists of three stages, which provides low noise, a highly stable detector bias, high photon current injection efficiency, high gain, and high speed. Several prototypes of 32×32 pixel bolometric detector arrays have been designed and fabricated. These arrays consist of detectors with lateral dimensions of 50μm 50μm, and each bolometric detector is on a 100μm pitch. The results of measurement show that the fabricated uncooled infrared focal plane arrays (UIRFPAs) have excellent performance. The frame rate is 50Hz, the pixel operability is above 96%, the responsivity (R) @ f/1 value is up to 15000V/W, the noise equivalent temperature difference (NETD) @ f/1 and 30Hz is about 50mK, and the average power dissipation is only 24.7mW. The results indicate that the technology of fabricating these 32×32 UIRFPAs has potential to be utilized for fabricating low cost and large-scale UIRFPAs.

1.55 µm spot-size converter integrated polarization-insensitive quantum-well semiconductor optical amplifier with tensile-strained barriers

A 1.55 µm polarization-insensitive lateral tapered spot-size converter integrated semiconductor optical amplifier (SSC-SOA) with tensile-strained barriers was investigated. The optical amplifier structure used a conventional ridge guide for the active layers and a second larger ridge for the passive waveguide. Low beam divergence of 12° × 15° results in about 3.1 dB coupling losses with −1 dB positional tolerances of ±2.3 µm and ±1.6 µm in horizontal and vertical directions using an anti-reflection coated flat-ended single-mode fibre. The active layer of SSC-SOA consisted of a tensile-strained barrier multiple-quantum-well structure. The SSC-SOA exhibited a signal gain of 25.5 dB and a saturation output power of 11.2 dB m with excellent polarization insensitivity (less than 0.5 dB) at 200 mA.