Takeshi Miyagi

An RF MEMS Variable Capacitor with Intelligent Bipolar Actuation

We propose an IBA scheme based on a pull-out detection, which is suitable for implementing in a circuit. The scheme is implemented in a driver IC that is part of a module with an RF MEMS variable capacitor. No failures are observed over 108 cycles at 85degC, which is an accelerated charging condition.

Electrical properties of a multilayer thin film substrate for multichip packages

The authors report the electrical properties of multilayer thin-film interconnects examined under circumstances in which the signal lines were sandwiched between mesh-pattern metal layers (called meshed stripline). Multilayer thin-film substrates with various transmission line structures were manufactured with several mesh patterns (power/ground planes) and signal lines, and the characteristic impedance and crosstalk for these lines were measured. The relations between the electrical properties and the meshed-stripline structures were obtained from the measurements for use in designing multilayer thin-film interconnects. It is shown that, in meshed-stripline structures, the characteristic impedance can be controlled by changing the aperture ratio or the mesh pitch. The fluctuation in the characteristic impedance along the signal-propagation direction was insignificant. It was also found that the crosstalk noise in meshed-stripline structures can be made as low as those in ordinary stripline structures.<<ETX>>

Robust hermetic wafer level thin-film encapsulation technology for stacked MEMS / IC package

This paper reports a thin-film encapsulation technology for wafer level micro-electro-mechanical systems (MEMS) package, using poly-benzo-oxazole (PBO) sacrificial material and plasma enhanced chemical vapor deposited silicon oxide (PECVD SiO) cap layer. This technique, which is applicable for MEMS technologies, saves die size and enables conventional package processes such as dicing, picking, mounting and bonding. Besides the fabrication processes of the thin-film encapsulation, this paper also presents the results of finite element models (FEMs) for the deflection and the mechanical stress of the thin-film caps. Moreover, in order to mount a MEMS chip with the thin- film capsulations and another integrated circuit (IC) chip that controls a MEMS chip in the same package, we have also developed an epoxy reinforcement technique for protecting the thin-film encapsulations and a topography wafer thinning technique for the MEMS chip. And then the system in package (SiP) for the MEMS and IC chips is fabricated successfully based on the mechanical analysis of the SiP process.

MCM-D/L using copper/photosensitive-BCB multilayer for upper microwave band systems

This paper describes an MCM-D/L technology for upper microwave band systems. The substrate of this MCM is constructed of copper/photosensitive-benzocyclobutene (P-BCB) multilayer formatted onto a print wiring board (PWB). Features of the developed MCM are (1) a novel microstrip structure for improvement of high-frequency characteristics and (2) a low-cost simple copper/P-BCB process using polishing technology. As BCB has good thermal and electric characteristics compared with polyimide or epoxy, BCB is expected to be applied to high frequency systems. We have developed a low-cost copper/P-BCB multilayer process with a new microstrip structure, and measured the high-frequency characteristics (10 GHz/spl sim/40 GHz). In the process technology, we took note of the adhesion of the metal film/BCB interface. As a result of a study of the adhesive metal and chemical/thermal treatment before and after fabrication of the film, we found that the necessary adhesion force was obtained by N/sub 2/ plasma treatment of the BCB surface before metal evaporation and annealing (250/spl deg/C:BCB cure temperature) after evaporation. Also, Cr was found to be the best material for adhesion. The high-frequency characteristics (10 GHz/spl sim/40 GHz) were estimated by a ring resonator and microstrip transmission line of copper/P-BCB multilayer fabricated on a PWB. Also, the S-parameters showed good characteristics. The developed MCM-D/L substrate has been proved to be suitable for high-frequency systems.

In-line wafer level hermetic packages for MEMS variable capacitor

In this paper, we report in-line wafer level hermetic packages (WLP) for MEMS variable capacitors. The beam structure of MEMS vibrates strongly under decompression. Since this vibration causes RF noise, it is necessary to set the pressure around the beam structure at 40000Pa or greater. Therefore, a structure that carries out a resin seal of the hole for etching the cap of a formed in the sacrificial layer process, at atmospheric pressure (101300Pa) is crucial for what. To prevent moisture permeation inside a cap, the resin was coated with a PECVD SiN layer. The developed packages become a hybrid hermetic encapsulation, which consists of PECVD SiN layers. Moreover, the deformation of the cap by external pressure was reduced using a corrugated cap. The developed package is comparatively large (340 times 1100 mum). Nevertheless, after the 265degC reflow test (5 times) and -55degC/125degC thermal cycle test (20 cycles), no cracks were observed in the packages. Since all of such processes and materials are compatible with the CMOS process, this package has very low cost. We present a summary of several aspects of our development activities in this MEMS variable capacitor packaging technology.

Highly reliable and manufacturable in-line wafer-level hermetic packages for RF MEMS variable capacitor

In this paper, we report a thin-film encapsulation technology for wafer-level micro-electro-mechanical systems (MEMS) variable capacitor package. The electrical characteristics of MEMS are adversely affected by moisture. In order to prevent moisture from permeating into a package, the top surface was protected with a plasma-enhanced chemical vapor deposition (PE-CVD) SiN layer. The developed packages become a hybrid thin-film hermetic encapsulation consisting of an internal shell using PE-CVD SiO, a seal layer coating with resin, and an external protective layer formed by PE-CVD SiN. The process is fully compatible with standard low-cost back-end-of-the-line (BEOL) technologies for LSIs as a wafer-level package (WLP). This hybrid structure was very effective for protecting the MEMS device from external moisture. Moreover, the electrode surface area has to be wide, because a wide range of capacities is necessary in MEMS variable capacitors. We have developed a large (1480 × 1080 µm) hermetic thin-film encapsulation as WLP.

Novel wafer-level CSP for stacked MEMS / IC dies with hermetic sealing

Novel wafer-level chip scale package (WL-CSP) applicable to configurations involving stacking of multiple dies has been developed. Since stacked die makes high topography and it is difficult to apply conventional WL-CSP process, gold bonding wires were used for not only connecting stacked dies with one another but also for connecting from each die to CSP terminals. The WL-CSP is also applicable to microelecrromechanical system (MEMS) that requires hermetic sealing. Thin-film encapsulation for MEMS was formed by conventional back end of line (BEOL) process. Followed by die stacking and gold wire forming, chemical vapor deposition (CVD) was applied to make hermetic sealing. The WL-CSP does not require photolithography process on topography wafer. It promises a cost-effective solution for MEMS/IC dies coupled device.

GaAs multichip module for a parallel processing system

A high-speed data transfer network for a parallel processing system has been developed on the basis of multichip packaging technology. The high-speed data transfer network connecting multiple processor units (PUs) has been achieved in a module using 8 bit-slice GaAs bus logic (BL) LSIs operating at 100 MHz. The GaAs multichip module consists of 12 GaAs BL LSIs in a 3*4 matrix. Each GaAs chip is sealed in a chip carrier with bumps. The chip carrier is flip-chip bonded to the copper/polyimide thin-film multilayer substrate. The characteristic impedance of the signal lines on the module is controlled to 75 Omega to be compatible with the GaAs original interface level. The thin-film termination resistors are made of Ni/Cr in the substrate to prevent reflections. A total power dissipation of 90 W of the module was efficiently radiated by a newly developed heat-pipe cooling module at 2-m/s air flow velocity with low acoustical noise. the total thermal resistance from the chip to the ambient medium was approximately 3 degrees C/W. A 3-Gb/s data transfer rate (32 b*100 MHz) can be realized by four stacked modules of 48 GaAs BLs. >

Millimeter-wave MEMS capacitive switch in vacuum-sealed in-line wafer level package

In this paper, we present a millimeter-wave microelectromechanical systems (MEMS) switch with a microsecond switching time. The optimization of the mechanical structure, application of high actuation voltages and encapsulation with a vacuum-sealed package result in a higher speed with which a beam of the MEMS switch is pulled in and pulled out. In order to reduce the packaging cost, we encapsulate the MEMS switch using an in-line wafer level package (WLP) which is built during the same complementary metal-oxide semiconductor (CMOS) process in which the MEMS switch is built. The fabricated MEMS switch is a shunt circuit and capacitive contact type. The dimensions of the in-line WLP are 500 µm wide by 500 µm long. The measurement results show an insertion loss of 0.5 dB and an isolation of 15 dB at a frequency of 50 GHz. The measured switching time is 2.0 µs or less. This is the shortest switching time of a MEMS capacitive switch for millimeter wave applications as far as the authors know.