Design of Atomic Force Microscope Cantilevers for Combined Thermomechanical Writing and Thermal Reading in Array Operation

King, W.P., Kenny, T.W., Goodson, K.E., Cross, G.L.W., Despont, M., Durig, U.T., Rothuizen, H., Binnig, G.K., and Vettiger, P., 2002, "Design of Atomic Force Microscope Cantilevers for Combined Thermomechanical Writing and Thermal Reading in Array Operation," IEEE/ASME Journal of MicroElectroMechanical Systems, pp. 765-774.

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In thermomechanical data writing, a resistively- heated atomic force microscope (AFM) cantilever tip forms indentations in a thin polymer film. The same cantilever operates as a thermal proximity sensor to detect the presence of previously written data bits. This paper uses recent progress in thermal analysis of the writing and reading modes to develop new cantilever designs for increased speed, sensitivity, and reduced power consumption in both writing and reading operation.  Measurements of cantilever electrical resistance during heating reveals physical limits of cantilever writing and reading, and verifies a finite-difference thermal and electrical simulation of cantilever operation. This work proposes two new cantilever designs that correspond to fabrication technology benchmarks.  Simulations predict that the proposed cantilevers have a higher data rate and are more sensitive than the present cantilever. The various cantilever designs offer single-bit writing times of 0.2 s–25 s for driving voltages of 2–25 V.  The thermal reading DR/R sensitivity is as high as 4 10 4 per vertical nm in near
steady-state operation. Analysis of the adaptable operation of a single cantilever bounds the operation of a cantilever array. The present cantilever operates with an array data rate as high as 35 Mbit sec 1 at a power of 330 mW and can operate at less than 100 mW. Proposed cantilevers offer a factor of 10 improvements in both data rate and power consumption. By considering their thermal, mechanical and electrical design, and by optimizing cantilevers for both writing and reading, this work aims to guide the future development of AFM cantilevers for thermomechanical data storage systems.

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