Development Of Transparent Lsco and Lscno Conductors for Optical Shutter Systems
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DEVELOPMENT OF TRANSPARENT LSCO AND LSCNO CONDUCTORS FOR OPTICAL SHUTTER SYSTEMS R. W. Schwartz, M. T. Sebastian, M. Charoenwongsa, and H. Dobberstein The Gilbert C. Robinson Department of Ceramic and Materials Engineering Clemson University Clemson, SC ABSTRACT We have prepared lanthanum strontium cobalt oxide (La0.50Sr0.50CoO3; LSCO 50/50) and lanthanum strontium cobalt nickel oxide (La0.50Sr0.50Co0.50Ni0.50O3; LSCNO) as candidate transparent electrodes for use in a shutter-based infrared sensor protection device. The shutter device requires that the electrode be transparent (80% transmission) and have moderate sheet resistance (300 Ω/sq.). Because of the effects of film thickness on intrinsic material properties, such as resistivity and extinction coefficient, and simple engineering issues (i.e., the relationship between film thickness, resistance and transmission), films of various thicknesses were prepared to achieve an optimal balance of electrical and optical performance. van der Pauw measurements and FTIR spectroscopy were used to study thin film properties. The best LSCO films prepared demonstrated electrical (438 Ω/sq.) and optical (68% transmission at 8 µm) properties that did not meet the target property goals for this application. However, the LSCNO films (of optimal thickness) offered performance (323 Ω/sq. and 73% transmission) close to the device requirements. INTRODUCTION Optical information obtained by sensors such as IR imaging systems is becoming of increasing importance in battlefield management. At the same time, the threat of damage to these optical systems has increased. The protection of sensor systems is therefore becoming more important. While the U.S. and other governments have agreed to prohibit the use of weapons that are designed to cause blinding, the use of tunable lasers by terrorist organizations still poses a significant threat to military personnel and sensor systems [1]. Hence, devices that provide optical limiting and serve to protect sensor systems that operate between 3 – 5 and 8 – 12 µm are of great importance to the U.S. Military. One sensor protection approach is an electrostatically driven shutter [2,3] placed in the optical path of the sensor, as illustrated in Fig. 1. A device, such as a photodiode, can be used to sense incoming threats and can activate to close the shutter for protection of the sensor. Stringent material requirements are placed on shutter components such as the substrate, electrode, and insulating layer. These layers need to be highly transparent to minimize the reduction in device sensitivity when the shutter is open, but the electrode must possess an adequate conductivity to electrostatically close the shutter. Target goals for the electrode are 80% transmission and a sheet resistance of 300 Ω/sq. This paper reports on the electrical and optical properties of lanthanum strontium cobalt oxide (LSCO) and lanthanum strontium cobalt nickel oxide (LSCNO) films prepared for the shutter-based sensor protection device. Although LSCO is known to be absorbing
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