Piezoresistive granular metal thin films of platinum–boron nitride and platinum–alumina at higher strain levels

Abstract

Granular metal thin films have a strain sensitivity much larger than continuous metal films. Experiments at high strain can help reveal their piezoresistive mechanisms. We deposit films of platinum nanoparticles in boron nitride (Pt:BN) as well as platinum particles in aluminum oxide (Pt:Al2O3) on polyimide foil as strain gauges. Under low strain of 0.1%, the films exhibit enhanced gauge factors, k=23 for Pt:BN and k=6 for Pt:Al2O3. Toward higher strain of 1.5%, Pt:BN shows reproducible and linear resistance-strain curves. In contrast, Pt:Al2O3 exhibits anomalies: The resistance-strain curves are highly nonlinear with an increasing slope before reaching saturation. The differential gauge factor versus strain increases from 9 to 9500, and the return curve shows large hysteresis. With scanning electron microscopy unstrained and in situ strained films are compared, Pt:BN shows no changes, whereas in Pt:Al2O3, large cracks develop. The relatively soft BN is less prone to cracks than the hard and brittle Al2O3. Hence, the gauge factor in Pt:BN can still be attributed to an electron tunneling mechanism, whereas Pt:Al2O3 becomes dominated by the influence of cracks. A model is presented, and we argue that the reproducible opening and closing of these cracks leads to the gigantic resistance increases at high strain.

Aerosol Jet Printing of Strain Sensors for Soft Robotics

“…In addition to the relative resistance change magnitude, consideration of resistance hysteresis is critical to produce reliable strain sensors. Piezoresistive strain sensors are usually associated with nonzero hysteresis [ 71 ] in their dynamic response to applied elastic strain and it is highly desirable to have as little hysteresis [ 72 ] as possible for practical applications. The first (plotted in red) and last (plotted in blue) representative strain hysteresis during the cyclic loading and unloading of each of the samples is shown in the corresponding subfigures (iii) in Figure 4.…”

“…The hysteresis observed in all the samples is less and comparable to those reported in the literature. [ 71,72 ]…”

“…The hysteresis observed in all the samples is less and comparable to those reported in the literature. [71,72] The quality factor metric or sensitivity of piezoresistive strain sensor is usually expressed as GF obtained as…”

Granular metals with SiN x dielectrics

“…GMs have been studied for >50 years [12,13] for both fundamental and applied research in nanoelectronics [14], plasmonics [15], superconductivity [16], and magnetism [17]. While GMs with various metals have been investigated, nearly all GM studies employed oxide-based insulators, such as SiO 2 , Al 2 O 3 , or yttria-stabilized zirconia (YSZ), with notable non-oxides including MgF 2 [18], BN [19], and carbon-based [20,21] GMs. Recently, we found that GMs with non-noble metals and oxide insulators form metal-oxides, which deleteriously increase GM conductivity at j < j c [5].…”