Wireless data transmitters with low power consumption are required for the Internet of Things (IoT) in general and medical sensors in particular. The energy supply of such transmitters is based on the use of batteries or inefficient energy generation from radio frequency (RF) waves.

THAWIT aims to develop the world's first wireless transmitter that is powered by compact, integrated thermoelectric energy generation. The following challenges must be overcome to enable self-sufficient operation. The energy consumption of the transmitters must be massively reduced, while the power density of the thermoelectric generator must be significantly increased. A key challenge here is integration in silicon, which limits the choice of possible material compositions. Research into silicon-compatible thermoelectric generators with a power density of over 10 μW/mm² at a moderate temperature difference of 7 K is one of the key challenges. To achieve this, the geometry and material compositions of the thermoelectric generator must be rigorously optimised. The high output power density requires a large leg length, which influences the choice of photoresist and the deposition parameters of the thermoelectric material. To reduce the thermal conductivity, a new process for the production of the p-doped legs is to be researched. In addition, we are developing a silicon-compatible energy storage device. To enable compatibility with the production technology/equipment at the IFW, this will be realised as a flat, high-performance interdigital micro-supercapacitor in silicon. The memory is based on photolithographically structured sputtered electrodes and a solid-state electrolyte.

Taking into account the charge losses that occur and an available chip area of 2 mm², the power consumption of the CMOS data transmitter must be around 10 µW. To enable this ultra-low power consumption, directly modulated oscillators with an aggressive duty cycle of 0.1 %, fast switch-on and minimised quiescent losses are being researched. In addition to impedance-matched antennas, inductive antennas that can be integrated directly into the LC resonator of the oscillator are being investigated. A textile-compatible, woven or printed antenna is being developed for the demonstrator. The demonstrator should fulfil the specifications of the Medical Implant Communication Service (MICS). The final goal is to demonstrate data transmission around 400 MHz with a data rate of 1-10 kb/s for distances of up to one metre.

THAWIT combines the complementary expertise of Gabi Schierning, IFW, in the field of thermoelectric components and Frank Ellinger, TUD, in the field of integrated RF circuits with low power consumption.

Waste products from silicon solar wafer and semiconductor production and applications are used to upgrade them through downstream process steps for use in various applications such as lithium-ion batteries, diodes, thermoelectrics or high-power ceramics.

The focus is on the material and process aspect:

The material must be characterised in detail with regard to further processing. This takes place in a gas phase reactor for nanomaterial production. The continuous conveying of large quantities of powder represents a process engineering challenge. In the reactor, the material is partially freed of impurities and, if necessary, doped. The resulting material is processed into demonstrators using laser beam melting (LBPF), which are electrically characterised in order to verify their usability for the above-mentioned applications.

In addition to the overall economic benefits, companies from the fields of PV recycling, plant engineering, material processing and LBPF end users in particular can benefit directly by expanding their existing manufacturing and product portfolio with corresponding technologies and components. Typically, these segments are often characterised by SMEs: reactors for nanomaterial synthesis, such as those used in this project, are the responsibility of plant manufacturers in the SME sector, as is the design and production of a powder conveyor. LBPF processes enable the prompt provision of functional prototypes and the near-net-shape production of complex components (with corresponding functional integration) that are difficult or impossible to manufacture using conventional production technologies. For SMEs in particular, this has the potential to make supply chains more flexible, reduce storage costs and bridge supply bottlenecks for certain products. The result is efficient on-demand production.