Graphene–Metal Composite Sensors with Near-Zero Temperature Coefficient of Resistance

Abstract

This article describes the design of piezoresistive thin-film sensors based on single-layer graphene decorated with metallic nanoislands. The defining characteristic of these composite thin films is that they can be engineered to exhibit a temperature coefficient of resistance (TCR) that is close to zero. A mechanical sensor with this property is stable against temperature fluctuations of the type encountered during operations in the real world, for example, in a wearable sensor. The metallic nanoislands are grown on graphene through thermal deposition of metals (gold or palladium) at a low nominal thickness. Metallic films exhibit an increase in resistance with temperature (positive TCR), whereas graphene exhibits a decrease in resistance with temperature (negative TCR). By varying the amount of deposition, the morphology of the nanoislands can be tuned such that the TCRs of a metal and graphene cancel out. The quantitative analysis of scanning electron microscope images reveals the importance of the surface coverage of the metal (as opposed to the total mass of the metal deposited). The stability of the sensor to temperature fluctuations that might be encountered in the outdoors is demonstrated by subjecting a wearable pulse sensor to simulated solar irradiation.

Laser patterned, high-power graphene paper resistor with dual temperature coefficient of resistance

“…The TCR value and its nature are two dening parameters of a device which decides whether it can be used as a temperature sensor or as a stable resistor in high-reliability circuits and systems. 21 More emphatically, in the case of temperature sensing applications, the device is supposed to show high TCR, on the other hand a resistor for reliable circuits must have a very low TCR. 22 The TCR of the printed resistor mainly depends upon the temperature coefficients of the ingredients of the ink along with the humidity and pressure of the surrounding environment.…”

Metallic Nanoislands on Graphene for Biomechanical Sensing

“…We were thus interested in how we might tune the composition of the metal−graphene composite films to achieve a similar effect. 15 In their pristine form, single-layer graphene has a negative TCR, while bulk metal has a positive TCR, and hence, the rates of change in resistance with respect to increasing temperature have the opposite sign. 16 By measuring the TCR of the films as a function of the nominal thickness of metal, we could generate films that were insensitive to temperature but not to strain.…”

Metallic nanoislands on graphene: a metamaterial for chemical, mechanical, optical, and biological applications

“…Using this strategy, we were able to minimize thermal drift in metal nanoisland-graphene composites by controlling the surface coverage of metal in the composite (Figure 4f). 54 This design strategy enabled the fabrication of a wearable sensor that exhibited stability against abrupt and large temperature fluctuations such as exposure to simulated sunlight (Figure 4g). Critically, this strategy used control of the materials—as opposed to backend electronics—to stabilize the signal.…”

“…Controlling the TCR minimizes thermal drift in wearable sensors as depicted in (g) which shows the thermal drift for three sensors after being heated by a solar simulator lamp. (f) And (g) reprinted with permission from 54 . Copyright © 2017, American Chemical Society.…”