The liquid compound bis(ethylcyclopentadienyl)tin, Sn(EtCp)2, was synthesized and exhibited several notable characteristics, including a vapor pressure suitable for use as a precursor and thermal stability up to 230 ℃. Using it as a precursor and O2 plasma as an oxidant, SnO2 thin films can be deposited by atomic layer deposition(ALD). A self-limiting reaction was confirmed with no nucleation delay for pulse times of 10 and 45 s for Sn(EtCp)2 and O2 plasma, respectively, at a growth temperature of 200 ℃. The growth per cycle(GPC)was 0.20 nm/cycle, which is higher than that of conventional precursors. Cross-sectional transmission electron microscopy revealed that the SnO2 film was uniform and polycrystalline, even though it was deposited at 200 ℃. X-ray diffraction analysis revealed that the film had a tetragonal rutile SnO2 structure with a(110)preferred orientation. Sn(EtCp)2 is a promising precursor for depositing high-quality SnO2 films with a stoichiometric composition, high purity, and high crystallinity, even at low temperatures.
For attachment to human skin of a MEMS tactile display device having arrayed actuators for mechanical stimulations, a Si substrate with arrayed through-silicon-via(TSV)electrodes and diode elements was fabricated for individual connection to each actuator without reverse current flow. After p-n junctions for the diode array were formed in a device layer of a silicon on insulator(SOI)wafer, deep holes(φ150 μm)for the TSV and 300-μm-deep large cavity were etched using a double-layered mask pattern from the substrate layer with deep reactive ion etching. After complete through etching from the device layer, sputtering and patterning of the Au/Cr seed film, Ni electroless plating was conducted to form the TSV electrode uniformly on the through-hole sidewall. A Pt/Ti/AlSi stacked thin electrode film was used to contact both the p-type and n-type Si surfaces of the diode. Instead of a long sintering process at 400 ℃ that causes shrinking and peeling of the Ni electroless-plated film, ohmic contact with low resistance was achieved between the Pt/Ti/AlSi electrode and the Si surface by rapid thermal annealing at 400 ℃ for 1 min or longer. The fabricated diode has low forward resistance and sufficiently high backward breakdown voltage greater than 35 V.