We have developed a 150°C technology for amorphous silicon thin-film transistors ͑a-Si:H TFTs͒ on polyimide substrates deposited by plasma enhanced chemical vapor deposition. The silicon nitride gate dielectric and the a-Si:H channel material were tailored to provide the least leakage current and midgap defect density, respectively. In addition, we conducted experiments on the TFT structure and fabrication with the aim of obtaining high electron mobility. TFTs with back-channel etch and channelpassivated structures were fabricated on glass or 51 m thick polyimide foil. The a-Si:H TFTs have an on/off current ratio of ϳ10 7 and an electron mobility of ϳ0.7 cm 2 /V s. Plastic substrate films for active electronic circuits are attracting increasing attention. Circuit fabrication processes must not exceed the glass transition temperature of the substrate. At present, the principal materials technology for thin-film transistors ͑TFTs͒ is based on silicon. We have been developing an amorphous silicon ͑a-Si:H͒ based TFT process with 150°C maximum temperature for compatibility with flexible polyimide foil substrates. A key component of the process is the deposition of the silicon nitride (SiN x ), which serves as the passivation layer for the substrate and as the gate dielectric. In conventional a-Si:H TFT fabrication, the SiN x is deposited at 300-350°C, which is the highest temperature step in the entire process and is needed to ensure low gate leakage current. Reduction of the SiN x deposition temperature from 350 to 150°C, while retaining low gate leakage, is a serious challenge.Plasma enhanced chemical vapor deposition ͑PECVD͒ is the standard technique for the fabrication of a-Si:H TFTs. A number of authors have reported silicon nitride films deposited by PECVD at a temperature lower than 250°C, 1-10 but only a few studies were aimed at process optimization. 8-10 Encouraged by the rapid growth of the liquid crystal display industry, several groups have worked on adapting the currently practiced a-Si:H TFT technology to various plastic substrates 11-16 by reducing the deposition temperature. In this paper we summarize the results of the optimization of PECVD silicon nitride deposition at 150°C using primarily the leakage current as the quality criterion, and show that high quality a-Si:H TFTs can be fabricated at this temperature. Silicon Nitride Deposition and Experimental ResultsThe SiN x films were deposited from mixtures of SiH 4 , NH 3 , and H 2 using 13.56 MHz PECVD at a pressure of 500 mTorr ͑ϳ67 Pa͒. All layers were deposited at 150°C and the silane and ammonia flows were kept constant at 5 and 50 standard cubic centimeters per minute ͑sccm͒, respectively. We varied the H 2 flow rate from 55 to 220 sccm and the plasma power from 5 to 50 W. The electrode area was ϳ250 cm 2 . Each layer was simultaneously deposited on a clean Corning 7059 substrate ͑for optical measurements͒, on Corning 7059 coated with Cr ͑for electrical measurements,͒ and on a p-type Si wafer of ͓111͔ orientation ͑for infrared measurements͒. M...

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A new method of preparation of radio-frequency superconducting quantum interference devices on MgB2 thin films is presented. The variable-thickness bridge was prepared by a combination of optical lithography and of the scratching by an atomic force microscope. The critical current of the nanobridge was 0.35 µA at 4.2 K. Non-contact measurements of the current-phase characteristics and of the critical current vs. temperature have been investigated on our structures.

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