Characterization of Short-Wavelength-Selective a-Si:H MSM Photoconductors for Large-Area Digital-Imaging Applications
Photoconductor-type photodetectors are attractive as sensors due to their compatibility with thin-film-transistor (TFT) fabrication processes. Since they exhibit photogain, photoconductor detectors have better or comparable responsivity and quantum efficiency (QE) compared to p-i-n photodiodes. In this paper, the operation of metal-semiconductor-metal photoconductor-based photodetectors using aluminum electrodes and thin hydrogenated amorphous-silicon (a-Si) films is investigated. The experimental results of photocurrent measurements, as well as the responsivity and QE for different a-Si film thicknesses, bias voltages, and electrode gaps, are presented. Integration with TFT fabrication and its application in large-area digital imaging are discussed.
Lateral Organic Semiconductor Photodetector. Part I: Use of an Insulating Layer for Low Dark Current
The thin flexible, lightweight nature of organic semiconductor devices makes them a prime candidate for medical imaging applications such as rugged X-ray imagers for use in hospitals (i.e., immune to minor drops or shocks) or even curved X-ray imagers for specialized imaging modalities of the future (e.g., compression free breast imaging). However, the performance of these organic sensors is not yet comparable with current technology (amorphous silicon) in particular owing to high dark currents. Here we show that the use of an insulator material, such as polystyrene, can dramatically improve the dark current performance of the organic photoconductor without compromising the device speed. Consequently, we are able to operate the sensor under high bias to achieve significant improvements in the critical parameters for image sensors such as photo-to-dark current ratio, sensitivity, dynamic range, and transient speed. Our work has the potential to expedite the adoption of organic semiconductor technology for a variety of digital imaging applications especially in the field of low-cost, portable biomedical equipment.
Third order nonlinear distortion of SAW duplexers in UMTS system
Nonlinearity distortion characterization and accurate modeling techniques for leaky surface acoustic wave (LSAW) devices have been desired in the recently years due to the applications of the Radio Frequency (RF) SAW duplexers in the third-generation (3G) telecommunication system, such as Universal Mobile Telecommunications System (UMTS). In the work, we first discuss the approaches to measure and characterize the 3rd order harmonic generation of the resonators on lithium tantalate YXl42° wafer and YXl48° wafer, with resonance frequency of 800MHz to 900 MHz; Second, we present an effective nonlinear Butterworth-van-Dyke (BVD) model to simulate the multi-tone 3rd order intermodulation effects of a band 5 duplexer; simulation result vs. measurement of 3rd order harmonic generation, 3rd order intermodulation (IMD3) and triple beat are presented.