Mitsutoshi Makihata

Adhesive wafer bonding using a molded thick benzocyclobutene layer for wafer-level integration of MEMS and LSI

This paper describes a wafer bonding process using a 50 µm thick benzocyclobutene (BCB) layer which has vias and metal electrodes. The vias were fabricated by molding BCB using a glass mold. During the molding, worm-like voids grew between BCB and the mold due to the shrinkage of polymerizing BCB. They were completely removed by subsequent reflowing in N2. After patterning Al on the reflowed BCB for the electrodes and via connections, bonding with a glass substrate was performed. Voidless bonding without damage in the vias and electrodes was achieved. Through the process, the control of the polymerization degree of BCB is important, and thus the polymerization degree was evaluated by Fourier transform infrared spectroscopy. The developed process is useful for the wafer-bonding-based integration of different devices, e.g. micro electro mechanical systems and large-scale integrated circuits.

An SOI tactile sensor with a quad seesaw electrode for 3-axis complete differential detection

This paper presents a novel SOI capacitive tactile sensor with a quad-seesaw electrode for 3-axis complete differential detection, which enables integration with a CMOS. For differentially detecting 3-axis forces, the tactile sensor is composed of four rotating plates individually suspended by torsion beams. In this study, to demonstrate the working principle, we fabricated a test device that integrates an SOI substrate with the quad-seesaw electrode and an anodically bondable LTCC substrate with fixed electrodes as an alternative to the CMOS. The experimental results of the test device successfully demonstrated the working principle as well as 3-axis differential detection with a matrix operation.

Integration and packaging technology of MEMS-on-CMOS tactile sensor for robot application using molded thick BCB layer and backside-grooved electrical connection

This paper describes a novel integration and packaging process for a chip-size-packaged integrated tactile sensor. A MEMS wafer and a CMOS wafer were bonded with a thick (50 µm thick) BCB (benzocyclobutene) layer, which also works as the dielectric layer of sensing electrodes. The large thickness is advantageous to reduce parasitic capacitance to the CMOS circuit. The thick BCB layer was formed on the CMOS wafer and molded with a glass mold to make a flat surface with via holes. For surface mounting, bond pads are located on the backside of the senor chip by drawing electrical feed lines through the chip edge. To make the feed lines in wafer level, tapered grooves were fabricated along the scribe lines by TMAH wet etching, and half dicing was done along the grooves to access electrodes on the BEOL layer. Finally, the tactile senor was completed and preliminarily evaluated.

Design and Fabrication Technology of Low Profile Tactile Sensor with Digital Interface for Whole Body Robot Skin

Covering a whole surface of a robot with tiny sensors which can measure local pressure and transmit the data through a network is an ideal solution to give an artificial skin to robots to improve a capability of action and safety. The crucial technological barrier is to package force sensor and communication function in a small volume. In this paper, we propose the novel device structure based on a wafer bonding technology to integrate and package capacitive force sensor using silicon diaphragm and an integrated circuit separately manufactured. Unique fabrication processes are developed, such as the feed-through forming using a dicing process, a planarization of the Benzocyclobutene (BCB) polymer filled in the feed-through and a wafer bonding to stack silicon diaphragm onto ASIC (application specific integrated circuit) wafer. The ASIC used in this paper has a capacitance measurement circuit and a digital communication interface mimicking a tactile receptor of a human. We successfully integrated the force sensor and the ASIC into a 2.5×2.5×0.3 mm die and confirmed autonomously transmitted packets which contain digital sensing data with the linear force sensitivity of 57,640 Hz/N and 10 mN of data fluctuation. A small stray capacitance of 1.33 pF is achieved by use of 10 μm thick BCB isolation layer and this minimum package structure.