Papers by Author: Shozo Inoue

Abstract: In this article, a new technique for controlling crack position and its propagation direction in solder-bonding using Al/Ni exothermic reaction is described. Sputtered Al/Ni multilayer film is able to produce heat instantly by its self-propagating exothermic reaction, and the reactive film can be used as heat source for solder-bonding. During the reaction, however, volume reduction by approximately 12% occurs due to crystal structural change from fcc to bcc and lattice-spacing reduction. Consequently, cracks are produced in the reacted NiAl structure. The cracks negatively affect the strength of the bonded system. We have found a new technique for controlling crack position and its propagation direction. Multiple ignitions for reaction demonstrated that cracks in reacted NiAl film can be controlled. When applying the flash heating technique to wafer-level bonding, cracks are probably produced. If cracks can be fabricated on dicing cut lines by using the simultaneous multiple reactions technique, crack-less solder-bonded Si hermetic packages would be realized.

Abstract: The purpose of this work is to establish a deposition process of Ti-Ni-Cu films showing shape memory effect in the as-deposited state. 5-µm-thick Ti₅₀Ni₃₅Cu₁₅ films have been deposited onto thermally oxidized (001) Si wafer by triple-source dc magnetron sputtering at various substrate temperatures. Their shape memory behavior were characterized by XRD, DSC measurements and thermal cycling tests under various constant tensile stresses. We have confirmed that crystalline films can be grown directly when the substrate temperature exceeds 400°C. The films deposited at higher than 450°C showed thermoelastic martensitic transformation and their M_s temperature slightly increased with increasing substrate temperature. Since their M_s temperature were found to be higher than 30°C, they can be used as an actuator at RT. These films were also found to have higher critical stress against plastic deformation than the post-deposition crystallized films. We have also tried to fabricate a prototype of micro-actuator and to characterize their actuation behavior and have confirmed that TiNiCu/SiO₂ double layered diaphragm showed an actuation response to a pulsed current of more than 100Hz.

Abstract: This paper describes evaluation of the strength in Ag-Sn-jointed Si specimens heated by Al/Ni film’s exothermic reaction. The reaction generates heat enough to melt Ag-Sn film for soldering. To measure the strength, four-point micro-bending test technique has been developed. The rectangular-solid Si specimens having a Ag-Sn/AlNi/Ag-Sn section were prepared by dicing the bonded Si-wafer under various pressure loads. A higher pressure yielded a better contact condition between Al/Ni and Ag-Sn so that heat-conduction improved; consequently Ag-Sn was melted sufficiently. Al/Ni reactive film has a potential as a micro-heater in soldering for MEMS.

Abstract: We have deposited the Ti-Ni-X films having various compositions while keeping the Ti content to be ~50at% by means of triple-source dc magnetron sputtering. All of the annealed films showed thermoelastic martensitic transformation. Ms temperature of the Ti-Ni-Pd films increased with increasing Pd content, and the highest Ms temperature of ~180°C was attained for the Ti-23%Ni-27%Pd film. On the other hand, Ms temperature of Ti-Ni-Cu films slightly increases as Cu content increases. The transformation hysteresis is decreased rapidly down to 15~20°C by adding Pd or Cu more than 10at%. Both ternary alloy films showed shape memory behavior during thermal cycling tests under various constant stresses. The critical stress against plastic deformation, c, of the Ti-Ni-Cu films is higher than that of the Ti-Ni-Pd films. The recoverable strain of these ternary alloy films is found to be ~2%. Actuation response by Joule's heat induced shape memory effect of Ti-Ni shape memory alloy films was slightly improved by the addition of Pd or Cu into the alloy.

Abstract: This paper describes novel MEMS probe card device, which is composed of silicon (Si) cantilever beams actuated by titanium-nickel (Ti-Ni) shape memory alloy (SMA) films. Since Ti-Ni SMA film can yield a higher work output per unit volume, Ti-Ni film-actuated Si cantilever beam is expected to be a MEMS probe card device providing large contact force between probe and electrode pad. The developed cantilever beam produces a contact force by not only cantilever bending in contact but also the shape memory effect (SME) of Ti-Ni film arising from Joule’s heating. The SME of Ti-Ni film containing Ti of 50.5 atomic (at.) % to 53.2 at. % can generate an additional contact force of 200 μN on average under applying an electric power of 500 mW to the film. Ti-Ni film-actuated Si cantilever beam would be a key element for successful MEMS probe card with larger contact force and smaller size.

Abstract: The purpose of this work is to quantitatively clarify the shape memory behavior of Fe-Pd films containing ~30at%Pd by thermal cycling testing under various constant stresses. Fe-Pd films (4 $m thick) were deposited onto Si wafers with thermally formed 1$m-thick SiO2 layer using a dual-source dc magnetron sputtering apparatus. The deposited films were all annealed at 900°C for 60 min followed by iced water quenching. Perfect shape recovery was observed for Fe-30.0at%Pd film when the applied stress was lower than 300 MPa. The maximum recoverable strain was ~0.6%. Fe-29.2at%Pd film, on the other hand, showed unrecovered strain after thermal cycling even if the applied stress was 40 MPa. XRD measurements of the Fe-29.2at% Pd film before and after thermal cycling revealed irreversible fcc-bct martensitic transformation that occurred during cooling process at a temperature around -80°C. The critical stress of Fe-Pd films, at which plastic deformation commences to occur, is higher for films with 30 at% Pd than for films with 29.2 at% Pd, which is practically advantageous. The Ms temperature of these films is lower than room temperature when no bias stress is applied, while it becomes higher than room temperature when appropriate bias stress is applied, obeying Clapeyron-Clausius law.

Abstract: This paper focuses on investigating mechanical properties of micron-thick polycrystalline titanium nitride (TiN) films. We propose a new technique that can directly measure lateral strain of microscale crystalline specimen by X-ray diffraction (XRD) during tensile test. The XRD tensile test can provide not only Young’s modulus but also Poisson’s ratio of TiN films. Micron-thick TiN films were deposited onto both surfaces of single crystal silicon (Si) specimen by r.f. reactive magnetron sputtering. Young’s modulus and Poisson’s ratio of Si specimen obtained by XRD tensile tests were in good agreement with analytical values. TiN films deposited at Ar partial pressure of 0.7Pa had the average values of 290GPa and 0.36 for Young’s modulus and Poisson’s ratio. The elastic mechanical properties of TiN films gradually decreased down to 220GPa and 0.29 with increasing Ar partial pressure up to 1.0Pa, regardless of film thickness. The change in the film properties with Ar partial pressure would be attributed to the change in the film density.