Yoshihiro Koshido

Moisture-resistant ZnO transparent conductive films with Ga heavy doping

Moisture-resistant ZnO transparent conductive films were formed with Ga heavy doping by off-axis-type rf magnetron sputtering. The resistivity of 12.4wt% Ga-doped ZnO is 1.3×10−3Ωcm and changes by less than 3% over a 2000h reliability test at a temperature of 85°C and a humidity of 85%. The crystal structural analysis of the heavily Ga-doped ZnO films indicates that the c axis grows along various directions, which is quite different from the conventional c-axis oriented growth. The effect of heavy doping is discussed based on the crystal structural transformation and carrier compensation by excess Ga segregated in the film.

Chip-size package piezoelectric component

A surface acoustic wave device includes a SAW having an IDT disposed on a piezoelectric substrate, a conductive pad connected to the IDT, and a bonding substrate, wherein the SAW is bonded to the bonding substrate such that a protective space of the IDT is provided. The bonding substrate includes a through-hole in which an external terminal connection member connected to the conductive pad and an external terminal are disposed. The SAW is bonded to the bonding substrate by an adhesive layer including a solder layer.

Wafer Level Chip Size Packaging Technology for Bulk Acoustic Wave Filters

Wafer level chip size packages (WL-CSP) have been successfully fabricated for bulk acoustic wave (BAW) filters. WL-CSP has been completed at the wafer level prior to dicing. Two silicon wafers are used as a die and a lid for chip size packaging. Both device and lid wafers have the same expansion coefficient and the package is strong enough to withstand the thermal stress. The package has a hermetic seal with copper-tin intermetallic bonding. The bonded wafers are then thinned by grinding. Via holes are formed by reactive ion etching (RIE) and filled by copper electroplating. The package has solder bumps on each terminal, ready for flip-chip assembly. We have succeeded to produce CSP-BAW filters with a hermetically sealed cavity, which is 840 micrometers squared and 280 micrometers in height including solder bumps.

A 180nm lift-off process for 5GHz band surface acoustic wave filters using an i-line reduction stepper

Using an i-line reduction stepper, we successfully realized a lift-off resist pattern with a 180nm line and space (L/S) resolution. This pattern was achieved by combining the multilayer resist (MLR) process that we originally developed and optimum dipole off-axis illumination (OAI). The technology extends to resolution limit of i-line photolithography from 250nm to 180nm resolution. Using this technology, we fabricated 180nm L/S Al electrodes for a 5GHz band surface acoustic wave (SAW) filter. The characteristics of the filter were demonstrated.