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

• Published in: Sensors and actuators. A. Physical. 2000-05, Vol.83 (1), p.47-53
• Main Authors: Thaysen, J, Boisen, A, Hansen, O, Bouwstra, S
• Format: Article
• Language: English
• Subjects: Atomic force microscope; Atomic force microscopes; Cantilever; Exact sciences and technology; General equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Physics; Piezoresistive sensor; Rocket tip; Scanning probe microscopes, components and techniques; Symmetrical Wheastone bridge; Transducers
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/S0924-4247(00)00299-5

We have developed a new generic platform for the fabrication of multipurpose microprobes with integrated piezoresistive read-out, built-in background filter and silicon tip. The probe fabrication is based on SOI wafers with buried boron etch-stop layers, which allow us to realize probes with fully encapsulated resistors and integrated silicon tips. The dimensions of the resistors are well defined and leak-current is eliminated. Probes with a force constant in the range of 0.8–4 N/m and with resonant frequencies in the range of 40–80 kHz have been fabricated. The probes typically display a deflection sensitivity of (Δ R/ R)z −1=2.4×10 −7 Å −1, and a force sensitivity (Δ R/ R) F −1=2.7×10 −6 nN −1. The change in resistance of the piezoresistors is detected by a highly symmetrical on-chip Wheatstone bridge arrangement. The measured noise level in the Wheatstone bridge is in good agreement with the calculated noise limit and a minimum detectable cantilever deflection of 0.3 Å has been predicted for a measurement bandwidth of 10 Hz. The symmetrical bridge configuration has been compared with a nonsymmetrical setup, and it is concluded that the symmetrical Wheatstone bridge significantly decreases nonlinearities in the output response. Finally, the probe has successfully been used for atomic force microscopy (AFM) imaging.