Sputtered Manganese Dioxide as Counterelectrodes in Thin Film Capacitors

Abstract

Manganese dioxide films were sputtered with resistivities as low as 0.3 ohm-cm. Ta-Ta2Os-MnO2-Metal (TMM) capacitors were fabricated and found to have dissipation factors of 0.008 at 1 kHz and 0.011 at 100 kHz. Leakage currents for the TMM capacitors were 10-gA when measured at 75V (33% of the anodizing voltage). By chemically removing the sputtered MnO2 from the capacitors and then replacing the counterelectrodes the effect of sputtering on the dielectric could be observed. It was found that rf -~ 2 kV d-c sputtering conditions increased the dielectric dissipation factor by ~20% while the 3 kV d-c ~ rf conditions caused a 50% increase in the dielectric dissipation factor. The sputtered MnO~ films were found to be 7-MnO2 and showed a conduction activation energy of 0.10 eV (• for 3 kV d-c -~ rf and 2 kV d-e ~-rf indicating that similar material has been deposited under both sputtering conditions.The use of manganese dioxide in thin film capacitors has been studied by McLean and Rosztoczy (1) and various techniques have been used to deposit the Independent variables manganese dioxide films. These methods include pyro-D-C lytic spraying (1), electroless deposition (2), reactive Pres-current sure drawn Grid evaporation (3), and reactive sputtering (4,5). The D-C + rf (/D (mA) used results of these studies, in general, were: (i) MnO2 is beneficial to thin film capacitor reliability and 20 40~ NO initial yield, (ii) the dissipation factor of the capaci-20 0 No 20 0 NO tors were an order of magnitude higher at 1 kHz than 20 45 +50v the equivalent Ta-Ta2Oh-Metal (TM) capacitor, (iii) 20 33 +hV 20 35 --25V the dissipation factor became much higher at higher 20 45 -lOOT frequencies, and (iv) the resistivity of the MnO2 was always >5 ohm-cm, if, in fact, MnO2 was deposited.The bulk of the work on Ta-Ta2Oh-MnOx-Metal (TMM) capacitors has involved only pyrolytically deposited MnOz films of high resistivity (,.~103 ohmcm) and the purpose of this study was to investigate the properties of TMM capacitors with sputtered MnO2 films. The effects of various sputtering conditions on dissipation losses in the dielectric, the effect of MnO2 on the dissipation factor, and the effect of counterelectrode area were studied. In addition to capacitance measurements, capacitor yields, and leakage current measurements were made for comparison with TM capacitors. ExperimentalThe manganese dioxide films were sputtered in a conventional, diffusion pumped vacuum system as shown in Fig. 1. The sputtering cathode was in two / \ equal area sections so the rf supply could be operated in the push-pull mode. The rf supply was operated at SUSSTRATE~ 7.5 mHz for the present experiments with a constant TAeLE ~ ~ ~---, --100W power input. The cathode-substrate separation ~ J was 6.3 cm. The cathode was 8 in. in diameter and SHUTTER---~ H ~__ ~------i made of electrodeposited Mn metal (99.5% Mn). J Three 7050 glass slides were mounted on the substrate table for each run. ~ ~ l The substrates were 1 in. • 3 in. glass slides with SPUTTERING' TO the tantalum a...

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