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Memory - MRAM


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Development of Methanol Based RIE Processes for Nanoscale Magnetic Device Etching


With device sizes reaching further into the nanoscale, many exciting advances are being made in the areas of magnetoelectronics, spin electronics, and hard disk drives (HDD), including the development of bit patterned media (BPM) and the realization of spin transfer torque (STT) devices, such as magnetoresistive random access memory (MRAM) and spin torque oscillators. As is the case with any advanced technology, a number of challenges exist in fabricating such devices. In terms of device size, features range from sub-50 nm for MRAM and STO devices to sub-10nm for ultra-high density BPM beyond 1 Tbit/in2. Anisotropic, defect free etching at these scales is often difficult to achieve with conventional techniques, such as ion milling, as the physical nature of the process often leads erosion and material redeposition that can damage the structure. Instead, reactive ion etching (RIE) techniques must be used to meet the challenge. In this study, we present research on the development of a new methanol based RIE technique for the anisotropic etching of nanoscale magnetic device structures. We discuss the ability of methanol RIE to etch Co, Fe, and Ni based magnetic alloys, as well as nonmagnetic materials, such as Cu, Pt, Ru, and more through the generation of volatile carbonyl compounds. Utilizing electron beam lithography for nanoscale pattern generation, we demonstrate the ability of methanol to etch numerous types of STT and HDD related device structures with feature sizes as small as 20nm using parallel plate and inductively coupled plasma (ICP) RIE processes. Throughout this presentation, we will discuss ability of methanol RIE to generate enhanced selectivity, minimal redeposition, and less etch induced damage or erosion relative to ion milling when using mask structures that include SiNx, Ta, TaNx, and Ti. The high selectivity of such masks allows for anisotropic deep pattern transfer. Thus far, we have demonstrated bulk film etch ratios of more than 90:1 for materials, such as Cu, and 20:1 for materials, such as NiFe relative to Ta. Furthermore, we have shown that the addition of 25-30% Ar can enhance etch rate, selectivity, and directionality even further, allowing us to achieve etch rates as high as 40nm/min for alloys, such as NiFe. These results, the promises of such a technique and the feasibility of sub-10nm dimensions will be discussed in detail throughout the presentation.

Author Matthew Moneck
Uploaded February 14, 2011

Current Driven Oscillation and Switching in Co/Pd Perpendicular GMR Multilayer


In this work, we demonstrate spin torque transfer (STT) induced magnetization oscillation and switching in metallic spin valves with Co/Pd electrodes of perpendicular magnetic anisotropy. The lateral size of the perpendicular SV pillar is around 80nm. The bottom Co/Pd multilayer, acting as a perpendicular spin-polarizing/reference layer, is relatively thick with a relatively strong perpendicular anisotropy and a switching field of 8 kOe. An in-plane spin valve is placed on the top for reading back magnetization oscillation of the middle Co layer, whose thickness is varied from 0.7nm to 3 nm. When the middle Co layer is thin, current driven magnetization switching is observed. When the middle Co layer is relative thick, perpendicular spin oscillation is clearly observed with oscillating frequency at 4GHz. The corresponding differential resistance (dV/dI) versus current curve exhibits a well pronounced dip.

Uploaded August 11, 2010

Abstract and Highlight

Abstract No abstract available.
Uploaded February 15, 2010

Perpendicular Spin Valves With In-Plane SAF Layer


We describe an experimental demonstration of current-induced magnetic reversal of nanopillars with perpendicular magnetic anisotropy integrated with an in-plane synthetic antiferromagnet (SAF) structure. The perpendicular anisotropy is induced by using a Co/Pd multilayer and the SAF is implemented with a Co/Ru/Co trilayer. The film was patterned with e-beam lithography and ion-milled through to form pillars with an elliptical cross section of 50 x 100 nm2. The resistance measurement showed a decreasing trend as the magnitude of injected current is increased, which may be attributed to the alignment of the in-plane SAF layer to out-of-plane direction, resulting in the three layers pointing in the same direction. A GMR ratio of 0.8% was obtained, and the critical switching current is typically less than 2 mA. These devices may be useful for the future implementation of perpendicular spin torque oscillators, where the SAF layer will serve as a sensing structure so that the oscillation can be readout electrically as resistance oscillation.

Author Cheow Hin Sim
Uploaded July 14, 2009

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