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Insulated-gate field-effect transistors (IGFETs) (Fig. 1) comprising pentacene as the semiconducting layer have been fabricated and studied previously.[1±5] The characteristics and performance of pentacene IGFETs make them competitive for applications requiring large area coverage, mechanical flexibility, and low overall cost. Such applications include thin-film transistor (TFT) switching devices for active matrix liquid-crystal displays (AMLCDs), where hydrogenated amorphous silicon (a-Si:H) TFTs are currently used, active matrix organic light-emitting diode displays (AMOLEDs), and low end data storage (e.g., smart cards and identification tags). Pentacene TFTs have produced the highest field effect mobility values reported for organic IGFETs. A mobility of 0.62 cm 2 V ±1 s ±1 and a current on/off ratio of 10 8 have been reported for devices comprising vapor-deposited purified pentacene films grown at substrate temperatures of approximately 120 C. [3,5] These values of mobility and on/off ratio are similar to the ones reported for a-Si:H TFTs. However, an operating voltage swing from ±100 to +100 V is required in order to achieve such high performance from pentacene devices. This is too high compared to a-Si:H and for any practical applications in general. [6] This shortcoming is also demonstrated by comparing the subthreshold slopes, s, of a-Si:H devices (about 0.5 V/decade) and those of pentacene-based IGFETs (5±12 V/decade). The best subthreshold slope value for pentacene IGFETs reported to date is s^1.6 V/decade. [5] This was achieved by the use of a self-assembled monolayer (SAM) of octadecyltrichlorosilane deposited between the SiO 2 insulator and pentacene. Still, the required voltage span had to be larger than 100 V for high mobility and high current on/off ratio to be achieved in addition to low s. Recently, a mobility of more than 1 cm 2 V ±1 s ±1 was reported for a pentacene-based device that also required high operating voltages (about ±80 V).[7]A dependence of the calculated mobility of pentacene IGFETs on gate voltage has been observed earlier. [2,8] In the present paper, we have used our understanding of the gate voltage dependence of mobility in pentacene devices [8] to demonstrate high-performance pentacene IGFETs exhibiting mobility similar to (a-Si:H) TFT, good current modulation, and excellent subthreshold slopes at operating voltages of about 5 V. For this purpose we used a relatively high dielectric constant e metal oxide film as the gate insulator, specifically barium strontium titanate (BST), deposited by means of chemical solution processing. The typical IGFET configuration is depicted in Figure 1. Pentacene films were deposited using vapor deposition. As-received pentacene (97+ % FLUKA Chemical Co.) was used. It has been shown previously that both mobility and current modulation (I on /I off ) increase when pentacene is purified before deposition.[5] Thus we expect that our results could be improved substantially by using purified pentacene. Further details on the vacuum chamber configu...

We report spin-dependent perpendicular transport in the magnetic trilayer junction structure La0.67Sr0.33MnO3/SrTiO3/La0.67Sr0.33MnO3. Large (factor of 5) changes of magnetoresistance induced by a field of ∼200 Oe are observed at 4.2 K. Junction I–V characteristics at low temperatures are consistent with a metal–insulator–metal tunneling process with a large spin-polarization factor of 0.81 for the conduction electrons. Above 100 K, a variable range-hopping conduction shunts out the magnetoresistance contribution. This second conduction channel comes from the impurity states within SrTiO3 barrier and therefore is not an intrinsic limit to the magnetoresistance performance of the device at high temperatures.

We have grown epitaxial films of the YBa2Cu307 -,compound on SrTi03 substrates. The superconducting critical current in these films at 77 K is in excess of 10 A/cm and at 4.2 K in excess of 10 A/cm'. PACS numbers: 74.70.Ya, 74.60.Jg Over the last fifteen months the superconducting transition temperature has increased by a factor of 4 to approximately 100 K. This development was initiated by the remarkable observations of Bednorz and Muller, ' who showed that in La2, Ba (Sr,Ca)Cu409, with the K2NiF4 structure, the superconducting transition temperature was in the range of 30-40 K. Shortly after these results were reproduced in a number of laboratories, Chu and his associates showed that the application of pressure increased the transition temperature to 52 K and, furthermore, in the Y-Ba-Cu-0 systems, transition temperatures as high as 100 K could be obtained. Over the last few months a very large number of publications have appeared addressing various aspects of superconductivity in these materials.One of the weak points that has often been cited about this class of superconducting materials is their small critical current. Although a number of publications have appeared on this subject, the value of the critical current is still small relative to the more familiar metallic alloys. For example, the highest published value at 77 K known to these authors is approximately 10 A/cm .The range of potential utility of these materials is determined by the critical current. We have prepared epitaxial films of these materials and find that the critical current at 4.2 K is in excess of 10 A/cm and at 77 K is in excess 10 A/cm . The value of 4.2 K compares favorably with some of the best metallic alloys and we believe it can be increased even further. Epitaxial films with a nominal composition of YBa2CU307, -were prepared by the evaporating of Y, Ba, and Cu from three separate electron-beam sources in a vacuum of approximately 10 to 10 Torr comprised primarily of 02. The substrate was SrTi03 with a [100] direction perpendicular to the plane of deposition. During deposition the substrate was kept atapproximately 400 C. The procedure for our making these films is similar to that described earlier. ' As deposited, the films showed a broad peak in the x ray diAraction pattern characteristic of a highly disordered or an amorphous atomic arrangement. These films were annealed at approximately 900 C in 02 to obtain epitaxial films. This was confirmed both by x-ray diA'raction and electron-microscopy examination. The c axis of the orthorhombic structure was primarily perpendicular to the plane of the film. However, a fraction of the film had crystalline orientation with the c axis in the plane of the film. In addition to the orthorhombic structure there were trace amounts of a second phase present. The details of the film structure will be described in later publications. Figure I shows the typical change in resistance with temperature of our samples. Perhaps the most notable feature of these data is the relatively sharp transiti...

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Epitaxial thin films of La1−x⧠xMnO3−δ(0≤x≤0.33) where ⧠ is a vacancy have been grown on (100) SrTiO3 substrates by pulsed laser deposition. The lanthanum deficiency results in self doping of the system without the need for divalent ion substitution. Both the films and the bulk targets used for deposition were ferromagnetic and showed giant magnetoresistance (GMR). The films increased in saturation magnetization Ms and Curie temperature Tc with increasing x. The Tc, however, was about the same as found in Cax substitutions. Bulk samples showed little change in Ms and Tc with vacancy concentration. Ms in bulk samples is about half the value found in the films which have theoretical saturations for x≥0.2. GMR in the films is a few hundred percent but the bulk values are 25% at H=1.8 T.

A high-resolution electron beam has been used to generate metal structures 8 nm wide and 10 nm high using ’’contamination’’ resist and dense metal patterns with 25 nm linewidths on 50-nm centers using PMMA resist. These resist materials together with standard deposition techniques and ion beam milling have been used to prepare a variety of structures on the order of nanometers in dimension. Present metal structure dimensions are limited by electron backscattering events in the substrate, the microstructure of the metallic thin film, and unknowns in the contamination resist process itself. The processing techniques are discussed as well as the preparation of substrates which are almost transparent to the electron beam.

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