AVS 45th International Symposium
    Nanometer-scale Science and Technology Division Wednesday Sessions
       Session NS+AS-WeM

Paper NS+AS-WeM4
Silicon Cantilevers for Ultrahigh-Density Data Storage

Wednesday, November 4, 1998, 9:20 am, Room 321/322/323

Session: Innovative Force, Near-Field Optics, and Tunneling Measurements
Presenter: A. Kikukawa, Hitachi Ltd., Japan
Authors: A. Kikukawa, Hitachi Ltd., Japan
H. Koyanagi, Hitachi Ltd., Japan
K. Etoh, Hitachi Ltd., Japan
S. Hosaka, Hitachi Ltd., Japan
Correspondent: Click to Email
In the past few years we have been working on applying atomic force microscopy (AFM) technologies in data storage. One of the most important issues is to increase the data transfer rate (DTR). Thus, it is required to increase the cantilever resonance frequency but keeping the spring constant sufficiently small. Also, an integrated sharp tip is required for reading the small recorded marks. The smallest one we have made so far is an equilateral-triangle cantilever 7 µm long and 0.1 µm thick. Its measured resonance frequency is 6.1 MHz, which is about two magnitudes higher than most of the cantilevers used in AFM, and the calculated spring constant is 0.75 N/m. It was fabricated from a SOI (silicon on insulator) wafer using anisotropic reactive ion etching (RIE) for cantilever shape etching, isotropic RIE for the tip etching, and KOH anisotropic etching for removing excess bulk silicon on the back side and making it a freestanding cantilever. The most difficult part in making such small cantilevers was to control the variation of their dimensions. They are caused mostly by the lateral variation of the wafer thickness and the alignment error (±4 µm at maximum) between the cantilever pattern defined on the active layer and the handling piece pattern defined on the bulk side. We reduced the variation to a sufficient level not by connecting the cantilever directly to the handling piece but by connecting the cantilever via a supporting region sufficiently thicker than the cantilever and whose shape was defined from the cantilever side. We also developed new type of optical lever that can focus the incident beam spot diameter as small as 5 µm and that can be operated with a bandwidth as wide as 10 MHz. From a noise characteristic analysis, the sensitivity of the system was obtained as 4.84 µrad at 10 MHz bandwidth which corresponds to 0.48 Å when a 10 µm long cantilever is used. That is, we now have basic technologies for demonstrating a DTR of 10 Mbps.