High-bandwidth piezoresistive force probes with integrated thermal actuation

Abstract

We present high-speed force probes with on-chip actuation and sensing for the measurement of pN-scale forces at the microsecond time scale. We achieve a high resonant frequency in water (1–100 kHz) with requisite low spring constants (0.3–40 pN/nm) and low integrated force noise (1–100 pN) by targeting probe dimensions on the order of 300 nm thick, 1–2 μm wide and 30–200 μm long. Forces are measured using silicon piezoresistors while the probes are actuated thermally with an aluminum unimorph and silicon heater. The piezoresistive sensors are designed using open source numerical optimization code that incorporates constraints on operating temperature. Parylene passivation enables operation in ionic media and we demonstrate simultaneous actuation and sensing. The improved design and fabrication techniques that we describe enable a 10–20 fold improvement in force resolution or measurement bandwidth over prior piezoresistive cantilevers of comparable thickness.

The Tactile Receptive Fields of Freely Moving Caenorhabditis elegans Nematodes

“…We calibrated each cantilever via Laser Doppler Vibrometry to determine its resonant frequency (f0, Hz) and spring constant (k, N/m) 28,29 .…”

Piezoresistive cantilevers for nanomechanical sensing

“…Tosolini et al [49] achieved a resolution of about 40 pN with cantilevers of 250 lm length  8 lm width (with 2 lm leg width)  0.45 lm thickness. Doll and Pruitt [50] achieved resolutions of 8-40 pN with probes of 35-100 lm length  1 lm width  0.30 lm thickness.…”

“…An additional advantage of N-type doping is that the maximum N-type piezoresistive coefficient (in the (1 0 0) direction) is a factor of 1.4 greater than the maximum for P-type (in the (1 1 0) direction). Indeed, Doll and Pruitt [50] used relatively low temperature phosphorus doping to define N-type piezoresistors on thin (300 nm) cantilevers for force probes. One can directly take advantage of the higher G factor for N-type doping if a V-shaped cantilever geometry at 45°is used.…”

“…The cantilevers are 30-200 lm long, 1-2 lm wide and 300 nm thick, and have integrated actuators, either thermal [50] or piezoelectric [128]. They demonstrated the measurement of mammalian cochlear hair cell mechanotransduction with sub-10 ls rise times in water.…”

Atomic Resolution Disk Resonant Force and Displacement Sensors for Measurements in Liquid

“…Piezoelectric and piezoresistive sensing, on the other hand, enable integration of sensing elements on the AFM cantilevers which significantly simplifies the experimental setup by eliminating the need for external sensing elements, precise system alignment and complex circuitry for operation [6]. However, such methods require complex fabrication processes and cannot compete with some of the conventional technologies in terms of sensitivity [6]- [8]. Taking advantage of high performance of microscale rotational mode disk resonators in liquid, this work presents an integrated and convenient (with fully electronic readout) force-displacement measurement technique that can be deployed in various environments (vacuum, air, and liquid) with higher sensitivities.…”