Atomic force microscopy probe with piezoresistive read-out and a highly symmetrical Wheatstone bridge arrangement

We have developed a new generic platform for the fabrication of multipurpos e microprobes with integrated piezoresistive read-out, built-in background filter and silicon tip. The probe fabrication is based on SOI wafers with b uried boron etch-stop layers, which allow us to realize probes with fully e ncapsulated resistors and integrated silicon tips. The dimensions of the re sistors are well defined and leak-current is eliminated. Probes with a forc e constant in the range of 0.8-4 N/m and with resonant frequencies in the r ange of 40-80 kHz have been fabricated. The probes typically display a defl ection sensitivity of (Delta R/R)z(-1) = 2.4 x 10(-7) Angstrom(-1), and a f orce sensitivity (Delta R/R)F-1 = 2.7 X 10(-6) nN(-1). The change in resist ance of the piezoresistors is detected by a highly symmetrical on-chip Whea tstone bridge arrangement. The measured noise level in the Wheatstone bridg e is in good agreement with the calculated noise limit and a minimum detect able cantilever deflection of 0.3 Angstrom has been predicted for a measure ment bandwidth of 10 Hz. The symmetrical bridge configuration has been comp ared with a nonsymmetrical setup, and it is concluded that the symmetrical Wheatstone bridge significantly decreases nonlinearities in the output resp onse. Finally, the probe has successfully been used for atomic force micros copy (AFM) imaging. (C) 2000 Elsevier Science S.A. All rights reserved.