Ag/BiSe memristors for sensor data storage: a novel concept for zero-power sense-log devices

This thesis presents sense-log devices, a novel type of zero-power logging sensor. Sense-log devices aim to bridge the gap between existing sensing solutions in the form of loggers with sampling circuits and non-reusable chemical indicators. They employ non-volatile resistive switching to store information about a change of an external quantity. The devices are reusable, do not require battery power and oer electronic read-out of the sensed value. Here, the aim is to use thermoelectric conversion to provide information about external heat-ux changes and store it in a memristor that can be read and reset after the sensed event. The main focus of this work are fabrication and characterization of memristors and the concepts for connecting them in a joint heat-ux sensing sense-log device. Based on the state of the art, bismuth selenide was selected to perform both memristive and thermoelectric functions. A bottom-up fabrication path using microfabrication and electrochemical deposition is presented, resulting in compact deposits suitable for use as device pillars. Changing the electrodeposition method to galvanodynamic pulses resulted in ner control of the stoichiometry, while variations in electrolyte concentrations and additives resulted in both orthorhombic, as well as mixed orthorhombic/rhombohedral crystallinity. Previously not reported with electrodeposited bismuth selenide, the memristors display a clear hysteresis in combination with a silver top electrode. The low switching voltages of 100 mV and 24 hour non-volatile retention of resistance show promising potential for storing information from converted thermal energy. Analysis of the current-voltage sweeps points towards Schottky and space-charge-limited current transport regimes, while geometrical scaling and top electrode investigations imply interface-type valence change mechanisms. Integration aspects towards a joint sense-log device are discussed, as well as the electrochemical tuning of memristors for a reduction of process ow steps and higher overall resistance ranges. A demonstration of resistive switching triggered directly by the voltage from a commercial thermoelectric generator conrm the suitability of the presented memristive devices. The outlook presents further possibilities for improving the memristive devices and expanding the sense-log concepts.