Yasuyuki Tanabe

A novel semiconductor capacitive sensor for a single-chip fingerprint sensor/identifier LSI

We describe a new semiconductor capacitive sensor structure and the fabrication process for a single-chip fingerprint sensor/identifier LSI in which the sensor is stacked on a 0.5-/spl mu/m CMOS LSI. To ascertain the influence of the fabrication process and normal usage on the underlying LSI, sensor chips were subjected to an electrostatic discharge (ESD) test, mechanical stress test, and unsaturated pressure cooker test (USPCT). ESD tolerance is obtained at the value of /spl plusmn/3.0 kV. To investigate mechanical stress, we carried out a tapping test. The sensor is immune to mechanical stress under the condition of 10/sup 4/ taps with the strength of 1 MPa. A multilayer passivation film consisting SiN under polyimide film provides protection against contamination such as water. Thus, under USPCT conditions of 130/spl deg/C, 80% humidity, and 48 h, the chips were not degraded. The tests confirm that the proposed sensor has sufficient reliability for normal identification usage.

Fabrication of Optical Microelectromechanical-System Switches Having Multilevel Mirror-Drive Electrodes

This work describes a practical and high-yield method of fabricating optical microelectromechanical-system (MEMS) switches. The method features the use of thick-plated gold multilevel interconnections for the mirror-drive electrodes and polyimide coating to protect the fragile and easily-movable micromachined mirror. The multilevel electrode developed was over 80-µm high providing enough space for the tilting mirror placed above it. Open-short circuit yield was 100% on 6-inch wafers. All the processes for fabricating the electrodes were carried out at under 310°C, meaning the electrodes could be successively formed after mirror-control large-scale integrated circuits (LSIs) were fabricated on a wafer. The fragile mirrors are sealed in polyimide during the fabrication processes. As this method protects the mirrors against the shock and damage caused by factors such as the dicing process, it enables 3-dimensional MEMS structures that have moving portions to be handled through conventional fabrication processes without the need for any special care. The static and dynamic characteristics of the optical MEMS switches fabricated are shown.

Method for testing electrostatic discharge tolerance for fingerprint sensor LSI

The measurement of electrostatic discharge (ESD) tolerance for a capacitive fingerprint sensor LSI in which the sensor is stacked on a 0.5-micrometers CMOS LSI is described. To compare the contact discharge method and air discharge method, we investigated the dependence of the ESD failure voltage on the distance between the sensor surface and ESD electrode for a conventional planar-type fingerprint sensor LSI. The ESD failure voltage decreased as the electrode approached to sensor surface and reached its lowest value when the electrode touched the surface. Therefore, we conclude that the contact discharge method is more suitable for evaluating ESD tolerance for fingerprint sensor LSI because the measurement condition is clearly defined and ESD failure value is the most critical. Moreover, we revealed that our proposed sensor LSI with the grounded wall (GND wall) has high ESD tolerance of over +/- 8.0 kV by the contact discharge method.

Effect of Ground-Wall Structure in Capacitive Fingerprint Sensor on Electrostatic Discharge Tolerance

This paper describes the electrostatic discharge (ESD) tolerance of capacitive fingerprint sensor or sensor/identifier LSIs in which the sensor is stacked on a CMOS LSI. The ground-wall structure that we proposed as a capacitive sensor structure for ESD tolerance was investigated. The contact discharge method was used for the fingerprint sensor ESD test. The dependence of ESD failure voltage on the distance between the sensor surface and the ESD electrode was measured. In the planar-type structure, ESD failure voltage decreased as the electrode approached the sensor surface and reached its minimum when the electrode touched the surface. Results for the ground-wall type show a high ESD tolerance regardless of the distance. Moreover, in the test on the fingerprint sensor and sensor/identifier LSIs, the ground-wall effect was obtained with a high ESD tolerance. In conclusion, it was revealed that fingerprint sensor LSI or the fingerprint sensor/identifier LSI with a ground-wall structure has a high ESD tolerance of more than ±20.0 kV.