Stability of Structure, Phase and Elemental Composition of ChemicallyDeposited and Electrodeposited Gold Layers in Multilayer SystemsAuchemically reduced; electrodeposited /Co-W/Cusputtered / Glass-Ceramics
The changes in the structure and elemental composition of Au and Co-W thin layers after thermal treatment of 200 h at 200-300 oC and 50 h at 450 oC were systematically studied using the X-ray microanalysis of scanning electron microscope XL-30 ESEN Philips. The phase stability was evaluated by X-ray diffraction (XRD). The electrodeposited Co-W layer (W 46.0-53.0 wt. % depending on the electrodeposition regime) is amorphous and maintains its amorphous state after heating at 200 oC for 200 h and subsequent heating (+) at 300 oC for 150 h. Co-W amorphous layers prevent interdiffusion of Au and Cu atoms and formation of intermetallics AuCu in the systems of layers Au chemically reduced; Au electrodeposited /Co-W/Cu sputtered / glass-ceramics. The chemically reduced 0.4 � m Au layers maintain their structure and phase in the systems of layers upon heating at 200 oC for 200 h and subsequent heating (+) at 300 oC for 50 h. The Au layer maintains its Au content 85-86 wt. % upon heating at 450 oC for 50 h, the cobalt content of the layer up to 8.6 wt. % and content of oxygen bonded to Au of 8.6 wt. %. The electrodeposited Au layers (0.8 - 1.0 � m) maintain their structure at heating at 200 oC and 300 oC for 200 h. After additional heating at 450 oC for 30-50 h gold content in the layer decreases from 98.4 wt. % to 85.0 wt. %, cobalt content increases to 7.6 wt. % and oxygen to 7.2 wt. %. Functional properties of the above multilayer systems deteriorate by mutual diffusion of metal atoms and formation of brittle intermetallics. The latter may give rise to the formation of monolithic films, cause the deterioration of mutual adhesion of the layers and complete reactions of the upper conducting Sn, Au layers with the base metal Ni, Cu, Ti, Sn (15, 16). This diffusion can worsen the properties of very thin (0.5-1.0 � m) metal layers electrodeposited on a Cu layer (1-2 � m) sputtered on glass-ceramics (15).
THERMAL STABILITY OF TI/PT/AU NONALLOYED OHMIC CONTACTS ON INN
Extremely low contact resistance of nonalloyed Ti/Pt/Au metallization on n‐type InN is demonstrated. The contacts were annealed at different temperatures up to 420 °C to investigate their thermal stability. A low contact resistivity of 1.8×10−7 Ω cm2 was measured at room temperature using the transmission line method. This was due to the extremely high doping level (5×1020 cm−3) in the InN. After 300 °C annealing, the contact resistivity increased to 2.4×10−7 Ω cm2. For 360 °C annealing, the contact morphology showed some degradation, but the contact resistivity was almost the same as at 300 °C. There was serious degradation of the contacts after 420 °C annealing. The morphology became very rough, and the contact and sheet resistances increased by factors of 3–5 times. This degradation is believed due to the decomposition of the InN film. The contact resistivities between n‐type epitaxial GaAs and InN were also investigated, and showed values around 10−4 Ω cm2.
Three dimensional SMA microelectrodes with clipping structure for insect neural recording
A microelectrode, with clipping structure for insect neural recording, was designed and fabricated by using a Shape Memory Alloy (SMA) thin film. The SMA thin films (TiNi: Titanium Nickel) are deposited by using RF magnetron sputtering, and patterned by HF-HNO/sub 3/ wet etching. The transformation temperatures of the SMA thin films measured 54/spl deg/C(A*) and 50/spl deg/C(M*). The SMA micro-electrode consists of one clipping structure (720 /spl mu/m/spl times/480 /spl mu/m) and two probes(600 /spl mu/m/spl times/70 /spl mu/m). The desired three-dimensional shape is given to the electrode by bonded wire while annealing. The SMA microelectrode can clip a nerve cord tightly, and neural activity from a living insect has been successfully recorded with this SMA microelectrode.