Masafumi Kimata

Wavelength selective uncooled infrared sensor by plasmonics

A wavelength selective uncooled infrared (IR) sensor using two-dimensional plasmonic crystals (2D PLCs) has been developed. The numerical investigation of 2D PLCs demonstrates that the wavelength of absorption can be mainly controlled by the period of the surface structure. A microelectromechanical systems-based uncooled IR sensor with 2D PLCs as the IR absorber was fabricated through a complementary metal oxide semiconductor and a micromachining technique. The selective enhancement of responsivity was observed at the wavelength that coincided with the period of the 2D-PLC absorber.

Wavelength selective wideband uncooled infrared sensor using a two-dimensional plasmonic absorber

Abstract. A wavelength selective wideband uncooled infrared (IR) sensor that detects middle-wavelength and long-wavelength IR (MWIR and LWIR) regions has been developed using a two-dimensional plasmonic absorber (2-D PLA). The 2-D PLA has a Au-based 2-D periodic dimple-array structure, where photons can be manipulated using a spoof surface plasmon. Numerical investigations demonstrate that the absorption wavelength can be designed according to the surface period of dimples over a wide wavelength range (MWIR and LWIR regions). A microelectromechanical system-based uncooled IR sensor with a 2-D PLA was fabricated using complementary metal oxide semiconductor and micromachining techniques. Measurement of the spectral responsivity shows that the selective enhancement of responsivity is achieved over both MWIR and LWIR regions, where the wavelength of the responsivity peak coincides with the dimple period of the 2-D PLA. The results provide direct evidence that a wideband wavelength selective IR sensor can be realized simply by design of the 2-D PLA surface structure without the need for vertical control in terms of gap or thickness. A pixel array where each pixel has a different detection wavelength could be developed for multicolor IR imaging.

Mushroom plasmonic metamaterial infrared absorbers

There has been a considerable amount of interest in the development of various types of electromagnetic wave absorbers for use in different wavelength ranges. In particular, infrared (IR) absorbers with wavelength selectivity can be applied to advanced uncooled IR sensors, which would be capable of identifying objects through their radiation spectrum. In the present study, mushroom plasmonic metamaterial absorbers (MPMAs) for the IR wavelength region were designed and fabricated. The MPMAs consist of a periodic array of thin metal micropatches connected to a thin metal plate with narrow silicon (Si) posts. A Si post height of 200 nm was achieved by isotropic XeF2 etching of a thin Si layer sandwiched between metal plates. This fabrication procedure is relatively simple and is consistent with complementary metal oxide semiconductor technology. The absorption spectra of the fabricated MPMAs were experimentally measured. In addition, theoretical calculations of their absorption properties were conducted usin...

Platinum Silicide Schottky-Barrier IR-CCD Image Sensors

A 64 × 32-element Si monolithic IR-CCD array with the improved PtSi/p-Si Schottky-Barrier (S.B.) detectors has been developed. The improvement of the photoyield was achieved by the structure with no interconnection metal over the detectors and the thinner PtSi film for the S.B. The physical mechanism of the higher photoyield is discussed taking into account the carrier reflection at interfaces (PtSi–Si and PtSi–SiN). The performance of the 64 × 32 IR-CCD was sufficient enough to obtain a thermal image in the 3 to 5 µm atmospheric window range.

Low-cost 320x240 uncooled IRFPA using a conventional silicon IC process

A 320 X 240 uncooled IR focal plane array (IRFPA) with series PN junction diodes fabricated on a silicon-on- insulator (SOI) wafer has been developed. Resistive bolometers, pyroelectric detectors and thermopile detectors have been reported for large scale uncooled IRFPAs, while the detector developed uses the temperature dependence of forward-biased voltage of the diode. The diode has low 1/f noise because it is fabricated on the monocrystalline SOI film which has few defects. The diode is supported by buried silicon dioxide film of the SOI wafer, which becomes a part of a thermal isolated structure by using bulk silicon micromachining technique. The detector contains an absorbing membrane with a high fill factor of 90 percent to achieve high IR absorption, and the readout circuit of the FPA contains a gate modulation integrator to suppress the noise. Low cost IRFPA can be supplied because the whole structure of the FPA is fabricated on commercial SOI wafers using a conventional silicon IC process.

Low-Temperature Characteristics of Buried-Channel Charge-Coupled Devices

The characteristics of buried-channel CCDs in the temperature range between 40 K and 300 K were studied. It was found that the transfer loss had a peak at about 130 K and increased rapidly below 90 K. In these specific temperature regions, the transfer loss depended on the clock period, the data cycle time and the clock fall time. The characteristics were analyzed based on free-charge transfer mechanisms and the Shockley-Read-Hall theory. The peak at 130 K was caused by a trap at the energy level 0.22 eV below the conduction band, and the increase below 90 K by the carrier freeze-out. Furthermore, the reduction of impurity concentration in the buried channel turned out to be an effective method of improving the transfer efficiency below 90 K.

A 512/spl times/512-element PtSi Schottky-barrier infrared image sensor

An infrared image sensor with video quality has been developed for thermal imaging in the 3-5-/spl mu/m infrared band. The array size is 512/spl times/512. The device uses a platinum silicide (PtSi) Schottky-barrier photodetector. The charge sweep device architecture is applied to obtain a large fill factor. The pixel has a two-level polysilicon and two-level aluminum structure with a minimum design rule of 2 /spl mu/m. The pixel size and fill factor area 26/spl times/20 /spl mu/m/SUP 2/ and 39%, respectively. The responsivity has been improved by use of a thin metal film and an optical cavity structure. The barrier height is 0.22 eV, which corresponds to the cutoff wavelength of 5.6 /spl mu/m. The device operates at the standard TV frame rate. The noise at 300 K with f/1.5 optics is limited by the shot noise of the detector, and the device has the capability of resolving a 0.11 K temperature difference. High-quality infrared imagery has been obtained with a prototype infrared TV camera using this device.

Compact Low-Voltage Operation Micromirror Based on High-Vacuum Seal Technology Using Metal Can

In this paper, we present the design, fabrication, and vacuum package of an electrostatic comb-drive resonant micromirror. The micromirror having a high resonant frequency suitable for a laser scanning display was fabricated using a silicon-on-insulator (SOI) wafer. An individual die which was an array of four micromirrors with a total size of 5.5 × 5.5 mm2 was diced from the SOI wafer by dry etching. The die was packaged in a transistor-outline-8 metal can with a window in a vacuum-packaging machine at a pressure of 10-4 Pa. To evacuate the residual gases generated after the package process, a nonevaporable getter was used in the metal can. The resonant frequencies of the fabricated micromirrors were 13 and 25 kHz, respectively. An optical rotation angle of about 10° was achieved at a low driving voltage of 5 V. Due to the decrease of air-friction loss, the operation voltage decreased by a factor of 32 compared with the voltage operated at atmospheric pressure. The operation pressure in the vacuum package was evaluated to be about 0.7 Pa from the amplitude and quality factor of the mirror oscillation. Moreover, several properties, such as the surface profile of the micromirror, were evaluated before and after the packaging. The durability of the packaged mirror was tested at temperatures of up to 75°C. The theoretical explanations about air friction were also described.

A 512 × 512 element PtSi Schottky-barrier infrared image sensor

An image sensor for thermal imaging in the3-5μm infrared band will be discussed. Device has a pixel size of26×20μm and a fill factor of 39% achieved by use of charge sweep vertical readout registers.

Room-temperature-operated infrared image CCD sensor using pyroelectric gate coupled by dielectric connector

A room-temperature-operated infrared (IR) image sensor with 64*32 infrared-sensitive MOS gates was developed by combining a pyroelectric thin plate with a Si charge-coupled device (CCD) by dielectric coupling. A pyroelectric plate is bonded to the Si CCD with an organic dielectric, and controls the Si surface potential of the MOS gate. The ability of the pyroelectric MOS gate to control the Si surface potential as a function of the IR signal is analyzed by taking account of both electrical charge and heat transfer. From this analysis, the design of the infrared sensing element is optimized. The pyroelectric materials used for the MOS gate were LiTaO/sub 3/ and PZT, and the organic dielectrics used were glycerin, di-n-butyl sulfone, nitroaniline, and P(VDF-TrFE). The basic characteristics of the pyroelectric gate of the CCD were obtained for several combinations of the pyroelectric and organic dielectric materials. >