A Metal Nanoparticle Thermistor with the Beta Value of 10 000 K

Abstract

NTC thermistor, metallic oxide powders are mixed with a binder and sintered under high temperature (T ≈400-1450 °C). This step is not energy efficient and, even worse, prevents its use in fields requiring low-temperature processing, e.g., a flexible thermistor. In addition, with the increasing demand for high sensitivity, further improving the performance of ceramic thermistors faces great challenges. Composites of conductive filler in the insulating matrix have been used to improve the sensitivity of the temperature sensor, because the conducting pathways can be disconnected/connected upon swelling/shrinking. However, the temperature window is really small since it has to work near the melting point of crystalline regions. [1] Inspired by the ultrasensitive temperature/heat perception of living creatures, ion-conductive materials have recently attracted considerable attention. [2] For example, a composite of plant cells and carbon nanotubes shows a record high temperature sensitivity due to the increase of "free" conducting calcium cation concentration upon heating. [2b] Various ionic conductive materials (hydrogel, [3] ionic liquid, [2c,4] iongel, [5] etc.) combined with different output modes (resistance, [5a,6] capacitance, [7] voltage, [8] etc.) enable these devices with not only high thermal sensitivity, but also multiple functionalities (flexible, [5b,9] stretchable, [6b,7a] self-healing, [3a,10] etc.), displaying potential applications in electronic skins, prostheses, robots, etc. However, these ionic devices usually require sophisticated fabrication procedures and many of them suffer from poor stability due to the involvement of solvent. Up to now, the widely used NTC thermistor based on these ion-conductive materials with ultra-high sensitivity has been scarcely demonstrated.Metal nanoparticles, because of their physical and chemical attributes, have long been used as elements for sensing various physical (pressure, [11] humidity, [12] temperature, [13] etc.), chemical (organic vapors, [14] metal cations, [15] anions, [16] etc.), and biological (oligonucleotides, [17] proteins, [18] cells, [19] etc.) signals and/or species. Compared with other sensing applications, detecting temperature with metal nanoparticles is usually less efficient. This is due to the measured low activation energy (≈tens of meV), [20] indicating insensitive of their conductance to temperature. It is feasible to adjust the temperature coefficient and sensitivity of metal nanoparticles by various ligand treatments. [21] This method shows a limited increase of the activation energy (100-200 meV) by just tuning the interparticle distance. However, when these nanoparticles are functionalizedThe thermistor, typically made from metallic oxides, is a type of resistor whose electrical resistance is dependent on its temperature. Despite the wide usage, the limitations of ceramic thermistors become increasingly apparent as devices with improved performances are sought and as new applications emerge. Herein, a thermistor that is s...

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