Kazuyo Endo

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.

Performance of 320 x 240 uncooled IRFPA with SOI diode detectors

We reported a 320 x 240 uncooled IRFPA with 40 micrometers pitch having diode detectors fabricated on an SOI wafer. Since the fabrication process of the SOI diode detector is compatible with the silicon IC process, only a silicon IC fab is necessary for manufacture of the FPAs. This enables mass production of low cost uncooled FPAs. This paper focuses on the performance of the FPA. In the previous paper, we proposed a novel infrared absorbing structure which offers a very high fill factor. Although this structure exhibited a high infrared absorption because of interference absorbing components incorporated in the structure, large thermal capacitance was an issue. Thus we have improved the infrared absorbing structure in the newly developed FPA. The improved absorbing structure has been devised making use of reflection of metal interconnections including diode metal straps. A thermal time constant of 17 msec has been achieved without degrading the responsivity compared with the conventional absorbing structure.

PtSi FPA with improved CSD operation

Over the past ten years we have been developing PtSi focal plane arrays (FPAs) using the charge sweep device (CSD). FPAs are going to high resolution and the power of the FPAs are on an upward trend. Now we have developed a low-power CMOS CSD scanner (LOCCS) for a high resolution FPA. The conventional CSD scanner operates at the same frequency as that of the horizontal CCD to prevent fixed pattern noise (FPN), and generates a frequency pulse higher than the minimum requirement. The LOCCS is a kind of CMOS dynamic shift resistor, which generates clock pulses for vertical signal transfer without the low frequency input pulses that cause FPN. Because the LOCCS generates multi-phase clock pulses, the power consumption can be reduced. We have fabricated test devices to evaluate the improved CSD operation by the LOCCS, and confirmed that the devices operate normally and the reduction of power consumption is in good agreement with the theory. We also applied the LOCCS to a 256 by 256 PtSi FPA and obtained thermal images.

Silicon infrared focal plane arrays

Using Si VLSI technology, we can fabricate various kinds of infrared focal plane arrays (FPAs) which cover spectral bands from short wavelength infrared to long wavelength infrared. The Si-based technology offers many attractive features, such as monolithic integration, high uniformity, low noise, low cost, and high productivity. We have been developing Si-based infrared FPAs for more than 20 years and have verified their usefulness.

Portable high-performance camera with 801 x 512 PtSi-SB IRCSD

We have developed an 801 by 512 element PtSi Schottky-barrier FPA with low-power multiphase CSD readout for a compact high performance infrared camera. The power consumption of this detector is about a half of the conventional IRCSD and the number of pixels is 1.5 times of that. The cryocooler is a high efficiency and compact size Stirling-cycle cooler that has also been developed for this imager at the same time. The cooling capacity is just match for the new IRCSD. This paper describes the basic imager design and features.

High Temperature Reliability of the SiC-MOSFET with Copper Metallization

We investigated the SiC-MOSFET with Cu metallization instead of conventional Al metallization to apply to high reliability power modules. As Cu has higher electrical and thermal conductivity, yield strength, and tolerance of its migration than those of Al, applying Cu to metallization and wire bonds will lead to longer lifetime for power modules. One of the major difficulties with Cu metallization is its high diffusivity into SiO2 and poly-Si which are used as gate oxide, interlayer oxide, and gate electrodes in SiC-MOSFETs, resulting in degradation of devices. We fabricated the SiC-MOSFET with Cu metallization and a diffusion barrier. We have successfully obtained good characteristics same as conventional Al metallization and demonstrated its high temperature reliability.