Materials issues in the integration of magnetic structures on CMOS-MEMS.

摘要

A MEMS-based data storage is being developed at CMU for low power, high access speed and low cost. Multi magnetic heads and their actuators are proposed to be fabricated on top of CMOS and to be released with proper masking. We describe the development of a magnetic head process integrated with a CMOS-MEMS process for actuator fabrication. Process integration depends on an understanding of the structure-process-properties relationship of many different processes. Several materials problems were encountered and solved in the course of the process development. The experiment work and rationale for particular choices is discussed.; Low stress (25 MPa), magnetically soft films of permalloy (Ni ₈₀Fe₂₀) were deposited for a MEMS-based data storage application without significant plasma-induced substrate heating. Optimization of film properties was performed using a designed experiment, response surface methodology. The relationship between the results of the factorial experiment is explained based on Murayama's stripe domain theory.; The properties of AMR sensors fabricated on structures released by the CMOS post process are characterized. The AMR sensor on the released MEMS structure functions properly and the MR head shows 0.4% MR change. According to our analysis of the required MR properties and its specification, the characteristics of TMR sensor, high intensity signal and low power consumption, well satisfy the requirement of MEMS-based data storage system. A TMR sensor has been built on our yoke type head. We have investigated the planarized surface with AFM for higher accuracy. The polishing mechanisms for oxide and permalloy are studied based on the materials corrosion theory using Pourbaix diagram. In addition, the uniformity of wafer and a cleaning process as a post CMP process were also studied. For simple fabrication processes, a photoresist layer was used as a side wall insulation which reduces process steps such as oxide or nitride deposition, lift-off and/or other additional etching processes. The sensor shows good tunneling I-V characteristics without shunting but it doesn't respond to the magnetic field. It is believed that the over oxidation would oxides the bottom electrode, permalloy, that ruins spin-preserved tunneling.