High-k Polymerized Dichlorotetramethyldisiloxane Films Deposited by Radio Frequency Pulsed Plasma for Gate Dielectrics i
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High-k Polymerized Dichlorotetramethyldisiloxane Films Deposited by Radio Frequency Pulsed Plasma for Gate Dielectrics in Polymer Field Effect Transistors Yifan Xu and Paul R. Bergera) , Department of Electrical and Computer Engineering The Ohio State University, Columbus, OH 43210 USA Jai Cho and Richard B. Timmons, Department of Chemistry and Biochemistry University of Texas, Arlington, TX 76019 USA ABSTRACT Polymerized dichlorotetramethyldisiloxane (DCTMDS) films deposited by radio frequency pulsed plasma polymerization (PPP) demonstrated very high dielectric constants for an organic-based system, in the range of 7 to 10. The high dielectric constants of PPP DCTMDS films are due to the high polarizability of the DCTMDS monomer. The pulsed plasma duty cycle (ON/OFF) resulted in higher dielectric constant DCTMDS films for higher duty cycles. The variation of dielectric constants does not show any trend with varying film thicknesses, indicating that the thickness of the deposited films is not significant for controlling permittivity. Post-deposition annealing in a certain temperature range improves the electrical integrity of PPP DCTMDS films, but temperatures that are too high induce even higher leakage than the samples with no heat treatment. An optimal annealing temperature was identified to be in the range of 150 oC to 200 oC. Samples annealed within this temperature window have low leakage current densities below 0.1 pA/µm2 at 10 V for film thicknesses about 100 nm. The PPP DCTMDS films are resistant to typical chemical solvents, and have withstood conventional photolithographic processing with no observable film shrinkage, warping or peeling. Film adhesion was excellent and withstood the scotch tape test. a)
Author to whom correspondence should be addressed. Also at: Department of Physics, The Ohio State University, Columbus, OH 43210; Electronic mail: [email protected] INTRODUCTION High-k gate dielectrics are highly desirable for any metal-insulator-semiconductor field effect transistors (MISFET) as the capacitance of the gate insulator scales with permittivity, which is in turn proportional to the field effect transistors (FETs) output current. A suitable polymer dielectric is needed that is flexible with high permittivity concurrently with low leakage current. The magnitude of the dielectric constant depends on polarizability of the insulator and its molar volume. The dielectric constant of organic materials can be predicted from its molecular dielectric polarizability, α, and the molar volume, Vm, according to the Clausius-Mossotti (CM) equation [1]: (1) K = (3Vm + 8πα)/(3Vm - 4πα). Polarizability is the ability of the polarizable units, namely electronic, atomic and dipolar, in a polymer to orient quickly enough in response to the oscillations of an alternating electric field. A higher dielectric constant is demonstrated by polymers with high polarizability. The exact
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prediction of molecular polarizability involves tedious calculations. However, a simple estimation of polarizability is t
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