An ultra-small tactile sensor with functions of signal processing and digital communication has been prototyped based on MEMS-CMOS integration technology. The designed analog-digital mixed signal ASIC allows many tactile sensors to connect each other on a common bus line, which drastically reduces the number of wire. The ASIC capacitively detects the deformation of a force sensor and sends digital data to the common bus line when the force exceeds a threshold. The digital data contain a physical ID of each sensor, 32-bit sensing data and 16-bit cyclic redundancy check (CRC) code. In this study, a novel wafer-level integration and packaging technology were developed, and a chip-size-packaged tactile sensor with a small footprint (2.5mm×2.5mm) and a low profile (0.27mm) was prototyped and tested. The sensor autonomously sends digital data like a tactile receptor of human.

The motivating principle behind this research is the development of small, wearable devices that would use humidity and temperature measurements as metrics for health monitoring. If it is to be useful as a health monitoring tool, the device needs to respond quickly and predictably to changes in humidity. Collagen is shown to be a viable humidity sensing material for use in capacitive relative humidity (RH) sensors. As a natural by-product of meat and leather industries, collagen presents itself as an interesting and inexpensive alternative to polyimide dielectric sensing materials. We used gelatin, a partially hydrolyzed form of collagen, to allow for easier spin coating. We have successfully fabricated devices by depositing a collagen thin film (1.2 μm) via spin coating, followed by Au/Pd electrodes (60 nm) via sputter coating. A plastic mask made from a rapid prototyping machine was used during physical vapor deposition (PVD) to pattern electrodes. This simple method eliminates the need for the use of more complicated photolithography processes. Interdigitated electrodes (rather than parallel plate electrodes) form a 6 mm wide, planar capacitor structure that has little dependence on dielectric thickness and is not affected by dielectric swelling. Initial findings indicate that these devices very closely match the results of the commercial relative humidity sensor used for reference. The capacitance-humidity relationship is shown to be non-linear, with an average change of 3 fF for every 1% change in RH around 60% RH, and an average change of 7 fF for every 1% change in RH around 80% RH. In this work, we present the fabrication and characterization of these novel collagen-based relative humidity sensors.

An approach to control the tensile stress and Q factor of thin Si film beams in MEMS resonators was investigated. Metal-induced lateral crystallization (MILC) using Ni nanoparticles that were synthesized within a cage-shaped protein, apoferritin, was applied to a thin morphous Si film for making a MEMS resonator with thin film beams. The MILC produced a thin polycrystalline Si (poly-Si) film with large crystallized domain (50-60 μm) with nearly the same crystalline orientation, whereas the poly-Si film obtained by conventional annealing (without MILC) consisted of small grains (less than 1 μm) with random orientation. The MEMS resonator with a beam made of poly-Si film by MILC was fabricated. The large domain size and the improved crystallinity increased the tensile stress, and resulted in 20% increase in Q factor in the resonant characteristics.

Diamond-like carbon (DLC) films as a new strain-capping material with compressive stress up to 12GPa for strained silicon technology were fabricated by filtered cathodic vacuum arc (FCVA) deposition system. The films’ compositions and bonding structures were characterized using multi-wavelength Raman spectroscopy. The relationship between intrinsic stress and G peak dispersion of the films’ Raman spectra were discussed. The results showed that the bias voltage applied to substrate during deposition determines films’ sp3 bonding content and intrinsic stress. Process compatibility of the DLC films with standard CMOS technology was confirmed by using WDXRF measurement. Also diffusion behavior of carbon atoms in DLC films with copper and silicon was studied with a Cu(200nm)/DLC(40nm)/silicon multilayer structure annealed at 500℃ in N2 atmosphere for an hour. At last, stress induced on silicon surface by DLC strips was characterized using surface sensitive UV-Raman spectroscopy. The results showed that DLC films with extremely high compressive stress have potential application in future CMOS strain engineering.

An inductor in standard CMOS process having an inductance of 52 nH and a quality factor of 1.5 at frequency equal to 80 Mhz was fabricated. The polymer passivation layer of the standard CMOS inductor was etched out. The silicon substrate under the inductor, having a thickness of 280 μm was also etched out by deep reactive ion etching (DRIE). Ferrite material ZnFe2O4 and amorphous material Fe4.7Co70.3Si15B10 was then sputtered on top of the inductor sequentially. The same sputtering procedure was also performed into the bottom of the inductor. The result is an inductor that is sandwiched by multiple ferromagnetic layers. The inductance of the new ferromagnetic inductor has increased by 15% from 52 nH to 60 nH. The quality factor has also increased by 20% from 1.5 to 1.8.

Crack free lead zirconate titanate (PZT) films for piezoelectric based MEMS devices have been prepared by a multiple coating sol gel process on platinized silicon (100) substrates. Rapid thermal annealing and Conventional furnace annealing were used for densification and crystallization of the amorphous PZT films. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Atomic force microscopy (AFM) were used to observe surface film morphology and grain growth. The phase content of the films was analyzed using X-ray diffraction. The role of intermetallics formed during the heat treatment in the growth of different orientations has also been observed. Film aging critical for device performance has been observed and methods to revert aging effects have been examined and discussed.

Resonators and switches are fabricated on LSI for advance wireless communication systems. In addition to surface micromachining, adhesive bonding has been applied for the fabrication. Lamb wave resonators are fabricated for multi-frequency oscillators by surface micromachining. Multi-band filters are formed by a MEMS process after bonding a Si wafer to a LSI wafer (wafer bonding first approach). SAW filters are made by bonding a MEMS wafer to a LSI wafer (wafer bonding last approach). Variable capacitors are fabricated on a piezoelectric LiNbO3 wafer. Wafer level packaging techniques are developed to encapsulate the MEMS on LSI. Open collaboration as shared wafer, prototyping facility and hands-on access fabrication facility are discussed to reduce a cost and a risk in the development of the MEMS on LSI.

This paper presents novel 3D heterogeneous integrations using MEMS Devices for RF applications. We propose a 3D heterogeneous integration method that combines the advantages of LTCC, passive integration, and MEMS technologies. The basic concept is to form a large-size LTCC wiring wafer and then to form high-Q passives or MEMS filters directly on the wafer surface. Other functional devices such as ICs, SAWs, and MEMS switches are mounted above the surface-formed devices. A miniaturized duplexer consisted of IPD, SAW, and film bulk acoustic resonator (FBAR); and a next generation duplexer module consisted of an MEMS tunable filter and a piezoelectric transducer (PZT)-actuated RF MEMS switch were constructed to demonstrate its feasibility and effectiveness.

Combinatorial sputtering is one of the useful methods that can be used to search for optimal composition of alloy materials or for new alloy materials. To search materials more efficiently, it is required that compositions and their distribution on samples can be easily controlled for the evaluation of their properties. Moreover, it is desirable that compositions change linearly to search for novel materials systematically. In conventional combinatorial sputtering method, it is difficult to fabricate samples having linear compositions distribution without moving hard masks or rotating substrate.

In this paper, a novel combinatorial sputtering method with New Facing Targets Sputtering (Combi-NFTS) of material search is introduced. In this method, several sputtering targets are placed in opposite direction, and substrates are placed in vertical direction of these targets. From this structure, thin film with binary/ternary composition distribution could be synthesized onto one single substrate. Moreover, it can fabricate samples having relatively linear composition distribution without moving hard masks or rotating substrate. As an example, Cu, Zr and Ti pure targets were used to confirm the performance of Combi-NFTS. Binary system of Cu-Zr and ternary system of Cu-Zr-Ti thin films were fabricated by using Combi-NFTS. After deposition, compositions of the films were characterized by the energy dispersive X-ray spectroscopy. As a result of Cu-Zr binary system, the composition of the thin film was changed as the power of targets was changed. Moreover, composition distribution was expanded as the distance from substrate to targets was decreased. In the Cu-Zr-Ti ternary system, it was obtained similar trend for composition distribution. Moreover, the composition changed two dimensional by changing the substrate position.

These results indicate that combi-NFTS can easily control the composition and composition distribution of thin films by changing the power of targets or the distance from substrate to targets which make combi-NFTS very suitable for combinatorial materials search.

This paper reports a NEMS (Nano Electro Mechanical Syetems) tunable color filter based on subwavelength grating with high color uniformity and low drive voltage. We newly proposed a GVG (Ground-Voltage-Ground) type tunable color filter deployed with a parallel-plate actuator with three pairs of electrode to decrease a crosstalk of an electrostatic attraction force between each actuator. The proposed structure was fabricated using an SOI wafer. The color tuning using was demonstrated by applying the drive voltage of 6.7 V. The reflected light intensity was decreased by 34 % at 680 nm wavelength. The color uniformity was also obtained in the filter area by reducing the variation of the displacement on one-dimensional arrayed actuators.

Post semiconductor manufacturing processes (PSM), including packaging and printed circuit board (PCB) manufacturing are now capable of producing trace widths of a few micrometers, high aspect ratio vias, three-dimensional constructions, and highly integrated systems in a single small package. Such PSM technology can in principle be used to manufacture micro electromechanical systems (MEMS) for sensing and actuation applications. Although MEMS are traditionally produced using silicon processes, the broad array of manufacturing approaches available in the packaging industry, including lamination, lithography, etching, electroforming, machining, bonding, etc., and the large number of available materials such as polymers, ceramics, metals, etc., provides greater design freedom for producing functional microdevices. The results of such processes applied to fabricating small systems are heterogeneously integrated MEMS devices. Since lamination of stacked layers is a critical component of this process, we refer to these devices as “laminate MEMS.”

In many cases laminate MEMS devices are more suited to their applications than their silicon counterparts, especially for applications such as biomedical, optical, and human computer interface. Furthermore, such microdevices can be built with a high degree of integration, pre-packaged, and at low cost. Indeed, the PCB and packaging industries stand to benefit greatly by expanding their offerings beyond serving the semiconductor industry and developing their own devices and products. This paper illustrates that good quality MEMS devices can be manufactured using packaging style fabrication, particularly using stacks of laminates, and discusses some of the unique benefits of such devices. This laminate MEMS technology promises not only improved methods for manufacturing microdevices but also for heterogeneously integrating them with silicon microelectronics and other components into a single package.

We have developed the tactile sensor using the microcantilevers with strain gauge film which can detect normal and shear forces simultaneously. In this work, the tactile sensor and the IC amplifier have been integrated heterogeneously to shorten the wire length by chip-on-chip stacking and reduce the noise in the output voltage. Standard deviation of the noise can be reduced from 27.6 mV to 3.3 mV by heterogeneous integration of the tactile sensor and the IC amplifier using Au wire bonding. By this heterogeneous integration, the device size and wiring numbers can be reduced, and installation of more sensors is allowed on fingertips of the robot. Moreover, through-silicon-via (TSV) holes were fabricated to mount an IC amplifier on the backside of the sensor chip, instead of using Au wires. Although TSV can be fabricated successfully, resistance to sacrificial etching process is problem. As a result, Si3N4 used instead of SiO2 has improved insulation between TSVs.

A 60 GHz tandem coupler using offset broadside coupled lines is proposed in a WLP (Wafer Level Packaging) technology. The fabricated coupler has a core chip area of 750 μm × 385 μm (0.288 mm2). The measured results show an insertion loss of 0.44 dB, an amplitude imbalance of 0.03 dB and a phase difference of 87.6° at 60 GHz. Also the measurement shows an insertion loss of less than 0.67 dB, an amplitude imbalance of less than 0.31 dB, a phase error of less than 3.7°, an isolation of more than 29.7 dB and a return loss of more than 27.9 dB at the input ant coupled ports and more than 14.3 dB at the direct and isolated ports over the frequency band of 57-66 GHz, covering 60 GHz band both in Japan and US. To the best of our knowledge the proposed coupler achieves the lowest ever reported insertion loss and amplitude imbalance for a 3-dB coupler on a silicon substrate. With its superior performance and lower cost compared to the CMOS counterparts, the proposed coupler is a suitable candidate for low-cost high-performance millimeter-wave systems.

Spray coating of a photoresist onto three-dimensional (3D) structure was investigated. To improve the uniformity of photoresist deposition onto the 3D structure, a shield plate with an aperture was used. The shield plate set over a sample permitted the resist deposition on the sample surface located in the aperture area while the plate blocked the deposition for the other area. The spray flow which is suitable for the resist deposition can be used effectively. Numerical analysis revealed that the vertical velocity component of gas flow was enhanced in the aperture area. In the experiments of the spray coating, the difference between the resist film thicknesses deposited on top and bottom trench surfaces was decreased. On the trench sidewall, resist bump formation, which was frequently observed in spray coating, was suppressed. The uniform resist deposition is necessary to realize 3D microdevices by lithography. In the microfluidic devices of dielectrophoresis, aside from the top and botttom trench surfaces, the trench sidewall can be used to fabricate device structures such as electrode for dielectrophoresis.

We developed an optimized inductively coupled plasma (ICP) etching process to produce GaAs pyramidal corrugated quantum well infrared photodetector focal plane arrays. A statistically-designed experiment was performed to optimize the etching parameters. The resulting parameters are discussed in terms of the effect on the etching rate and profile. This process uses a small amount of mask corrosion and the control of the etching mask gap to give a 45-50 degree V-groove etching profile, which is independent on the crystal orientation of GaAs. In the etching development, scanning electron microscope (SEM) was used to observe the surface morphology and the pattern profile. In addition, X-ray photoelectron spectroscopy (XPS) was utilized to obtain the elemental composition and the contamination of the etching surface. It is found that extremely small stoichiometric change and surface damage of the etching surface can be achieved while keeping relatively high etching rate and ~45 degree V-groove etching profile. This etching process is applied to the fabrication of pyramidal C-QWIP FPAs, which is expected to have better performance than the regular prism-shaped C-QWIPs according to electromagnetic (EM) modeling. The expected results will be verified by optical and electrical measurements. In addition to infrared detectors, this process technology can also be applied to GaAs V-groove solar cell, quantum wire light-emitting diodes, quantum wire lasers, and other GaAs –based devices.