A high-performance 801x512-element PtSi Schottky-barrier infrared image sensor has been developed with an enhanced Charge Sweep Device (CSD) readout architecture. In the enhanced CSD, the power consumption of the CSD has been reduced by employing a multiphase CSD with an on-chip multiphase CMOS clock generator. Flexible vertical scan is also possible using a newly developed transfer gate scanner. A large fill factor of 61% is obtained in spite of the small pixel size of 17x20 μm^2. The differential temperature response and noise equivalent temperature difference with f/1.2 optics at 300 K were 2.2x10^4 electrons/K and 0.037K, respectively. The saturation signal level was 2.1x10^4 electrons and the total power consumption of the device was about 50mW.
A 16x16 monolithic pyroelectric infrared image sensor has been developed. The image sensor utilized an electrospray (ESP) deposited polyvinylidene fluoride (PVDF) thin film as a pyroelectric material, a buried channel MOSFET as a low noise detection device, and a micromachined four-beams supported membrane as a thermal isolation structure. A voltage sensitivity of 6600 V/W and a detectivity of 1.6x10^7 cmHz^<1/2>W^<-1> have been realized with a sensing area of 75 μmx75μm at a chopping frequency of 55Hz. A thermal image of the circular window of a black body furnace has been successfully obtained. These results offer the promising prospect of a monolithic pyroelectric IR image sensor, although uniformity in voltage sensitivity, noise and offset voltage still remain to be improved.
Development of uncooled infrared camera has been accalerated to be improve its operating performance and to promote downsizing by production technology of integrated ciurcuit. It is the first time in Japan that the uncooled camera is realized, which employs 256×256 uncooled bolomater sensor elements. Vanadium Oxide material is selected for the uncooled bolometer sensor whose element size is 50μm×50μm and formed on the diaphragm bridge structure. As a result, it has a NETD of 0.2K with an f/1.0 lens at 30 frames per second.
We have studied the photocurrent multiplication in hydrogenated amorphous silicon-based Au/p-a-SiC : H/a-Si : H/n-c-Si structure photodiodes. They were fabricated on n c-Si substrate with the different impurity concentration, using an electron cyclotron resonance microwave plasma chemical vapor deposition (ECRPCVD) system. The photocurrent dependency on impurity concentration of the n c-Si were evaluated, and the photocurrent multiplication were observed only in the sample of about impulity concentration of 2×10^<16>cm^<-3>. The wavelength dependency on the incident light suggests that the photocurrent increase was caused by the avalanche multiplication in the a-Si : H layer.
The photocurrent multiplication due to impact ionization was observed in the a-Si : H/a-SiC : H staircase photodiode. On the staircase photodiode with one band offset, the photocurrent was multiplied double and was saturated. It was confirmed that almost all electrons were multiplied after they crossed the band offset. On the staircase photodiode with 3 band offsets, the saturated multiplication gain of about 6 was also obtained. The gamma values of the photocurrent characteristics were 1.0 indicating that there were no excess carriers entering from the electrode and no interband tunneling affected on photo-induced current. These results suggested that the impact-ionization at each conduction band stop due to the conduction-band discontinuity may be the dominant mechanism of the photocurrent multiplication.