Ryutaro Maeda

Effect of Surface Roughness on Room-Temperature Wafer Bonding by Ar Beam Surface Activation

Using Ar beam etching in vacuum, strong bonding of Si wafers is attained at room temperature. With appropriate etching time, the bonding occurs spontaneously without any load to force two wafers together. However, surface roughness of the wafers increases during Ar beam etching. Because surface roughness has a strong influence on wafer bonding, long etching time degrades the bonding strength. Using atomic force microscope, we measured surface roughness enhancement caused by Ar beam etching, and investigated the relationship between surface roughness and bonding properties such as strength and interfacial voids. The results agree well with theoretical predictions using elastic theory and energy gain by bond formation. A guideline for successful room-temperature bonding is proposed from these results.

Jet molding system for realization of three-dimensional micro-structures

Abstract We have developed a fabrication technology for realization of three-dimensional microstmctures composed of different materials using excimer laser ablation and ultrafine particle (UFP) jet molding. We have named this technology the jet molding system (JMS). This method enables the production of three-dimensional microdevices composed of actuator, sensor materials (PZT), and electrodes (metal). Insertmolding and mask-deposition methods were applied to obtain these structures. SEM observation as well as density and electrical property measurements showed good pattern transfer fidelity with sufficient deposited layer quality (density of better than 85%, dielectric constant of deposited PZT layer of 760). The deposition rate of PZT was much faster than that obtained using any other deposition technique, and a PZT layer up to 40 μm of thick was formed with the desired metal electrode structure.

Room-temperature microfluidics packaging using sequential plasma activation process

A sequential plasma activation process consisting of oxygen reactive ion etching (RIE) plasma and nitrogen radical plasma was applied for microfluidics packaging at room temperature. Si/glass and glass/glass wafers were activated by the oxygen RIE plasma followed by nitrogen microwave radicals. Then, the activated wafers were brought into contact in atmospheric pressure air with hand-applied pressure where they remained for 24 h. The wafers were bonded throughout the entire area and the bonding strength of the interface was as strong as the parents bulk wafers without any post-annealing process or wet chemical cleaning steps. Bonding strength considerably increased with the nitrogen radical treatment after oxygen RIE activation prior to bonding. Chemical reliability tests showed that the bonded interfaces of Si/Si could significantly withstand exposure to various microfluidics chemicals. Si/glass and glass/glass cavities formed by the sequential plasma activation process indicated hermetic sealing behavior. SiOx Ny was observed in the sequentially plasma-treated glass wafer, and it is attributed to binding of nitrogen with Si and oxygen and the implantation of N2 radical in the wafer. High bonding strength observed is attributed to a diffusion of absorbing water onto the wafer surfaces and a reaction between silicon oxynitride layers on the mating wafers. T-shape microfluidic channels were fabricated on glass wafers by bulk micromachining and the sequential plasma-activated bonding process at room temperature

Development of bi-directional valve-less micropump for liquid

A micropump based on a novel flow rectification principle was developed. Instead of mechanical check valves, the difference of flow resistance in narrow channels caused by the temperature dependence of liquid viscosity is utilized as the basis of the valve effect. This method allows a flexible control of the pump function, including bi-directional pumping. A prototype device actuated by a piezoelectric element was designed and fabricated to confirm the pump function. The fluidic and thermal conditions for the pump actuation, and the characteristics of its behavior revealed by experiments are discussed.

Development of phases and texture in sol-gel derived lead zirconate titanate thin films prepared by three-step heat-treatment process

Lead zirconate titanate (PZT) films were fabricated by the addition of 10 mol% excess Pb to the starting solution which was spin-coated onto Pt/Ti/SiO2/Si substrates. The effect of film thickness on texture was investigated, and it is clear that the (100) texture gradually increases and the (111) texture decreases with increasing film thickness. A PtxPb intermetallic metastable phase was observed by X-ray diffraction, and it is found that the position of this peak shifted from 38.30° 2θ (d : 0.2348 nm) to 37.10° 2θ (d : 0.4213 nm) with increasing firing temperature from 350°C to 550°C. The (111) preferred orientation in the PZT film was promoted by the metastable PtxPb phase. The formation of the (100) texture of perovskite phase in the multilayer films was mainly attributed to the effects of both substrates and crystal growth rates which depend on the crystal orientation.

Novel multibridge-structured piezoelectric microdevice for scanning force microscopy

In this article we report the structure and the microfabrication method of a novel micro-scanning force microscopy (SFM) device. It is a lead zirconate titanite (PZT) bimorph structure in the shape of a cantilever supported by bridges. Electric fields applied to the separated sections of the electrodes on the levers can induce lever deflection and actuate the tip in x, y, and z directions. The cantilever can vibrate and sense its own vibration amplitude to detect the surface topography in the cyclic contact SFM mode. In the fabrication process, the sol–gel method is modified for constructing high quality PZT films 3 μm thick. The single bridge device has shown microscopy sensitivity of 0.32 nA/nm in a vertical direction, with actuation sensitivities of 70–80 nm/V in a lateral direction. The multibridged structure has been proven to be effective in elevating the eigenfrequency, which is very important for improving the SPM data rate.

Ultrasonic micromixer for microfluidic systems

This paper describes the design, fabrication and evaluation of an active micromixer. Mixing occurs directly from ultrasonic vibration. The intended use of the device was for integrated micro chemical synthesis systems or for micro total analysis systems. The pattern of inlets, outlet and mixing chamber were formed in glass. The whole flow path was encapsulated by anodic bonding of a Si wafer to the glass. A diaphragm (6 mm/spl times/6 mm/spl times/0.15 mm) was etched on the Si side for oscillation. The ultrasonic vibration originated from a bulk piezoelectric PZT ceramic (5 mm/spl times/4 mm/spl times/0.15 mm), which was excited by a 60 kHz square wave at 50 V (peak-to-peak). Liquids were mixed in a chamber (6 mm/spl times/6 mm/spl times/0.06 mm) with the Si oscillating diaphragm driven by the PZT. A solution of uranine and water were used to evaluate the mixing effectiveness. The entire process was recorded using a fluorescent microscope equipped with digital camera. The laminar flows of uranine solution (5 /spl mu/l/min) and water (5 /spl mu/l/min) were mixed effectively when the PZT was excited.

Fabrication of three dimensional micro structure composed of different materials using excimer laser ablation and jet molding

Fabrication technology was developed for realization of three dimensional micro structure composed of different materials using excimer laser ablation and ultra fine particle jet molding. This method enables micro devices composed of actuator and sensor materials (PZT) and electrodes (metal). SEM observation and density and electrical property measurement showed a good pattern transfer fidelity with sufficient deposited layer quality (density of better than 85%, dielectric constant of deposited PZT layer of 760). Deposition rate of PZT was much faster than any other deposition techniques and up to 40 /spl mu/m of thick PZT layer was successfully formed with proper metal electrode structure.

Structure and electrical properties of multilayer PZT films prepared by sol–gel processing

Abstract Multilayer PZT(Zr:Ti=52:48) films were prepared by the repeated process of spin-coating and firing at 600°C of a PZT sol with various heating rates between 20 and 200°C min −1 . Their structural and dielectric properties were examined. The multilayer film prepared with the heating rate of 50°C min −1 shows the highest dielectric constant and a smooth surface with no surface cracks. High-resolution TEM (HRTEM) observations of an as-deposited PZT film indicate nucleation of perovskite and pyrochlore crystals in the amorphous matrix. The perovskite crystals are found to form through the initial construction of {110} planes.

Tip-Scanning Dynamic Force Microscope Using Piezoelectric Cantilever for Full Wafer Inspection

In this study we demonstrate the structure of a new dynamic force microscope (DFM) compatible with full wafer inspection. It is a tip-scanning-type DFM based on a piezoelectric micro-cantilever integrated with a conical tip as a force sensor. The piezoelectric micro-force sensor is mounted on top of a tube scanner. The sample is put on the sample stage facing the tip. The novel DFM has proven to be stable for probing the surface of full wafers with a vertical resolution of about 0.12 nm. The design and performance of the novel tip scanning DFM is explained in detail in this report.