Thermoelectric generator based on ultrathin Si thin films. Design, fabrication and characterization

Objective
Develop a planar micro‑TEG using ultrathin (~70–100 nm) Si films, CMOS‑compatible, fabricated on Si-on-insulator (SOI) substrates, to harvest low-grade waste heat for low‑power applications (µW–mW range).

Device Design

Utilize SOI wafers featuring a (~70-100 nm device Si layer). Pattern arrays of suspended Si membranes (tens of µm lateral dimensions) alternately doped n- and p‑type (e.g. phosphorus and boron at ~10^20 cm−3), electrically in series and thermally in parallel, forming miniaturized thermocouples. Introduce nanostructure features (nanopores, phononic lattices, corrugations) to reduce thermal conductivity while preserving electrical conduction, enhancing the power factor and effective ZT.

Characterization Methods

• FEM models for geometry and termal optimization.
• Seebeck coefficient (S): measured via induced voltage across arrays under controlled ΔT.
• Electrical and thermal conductivities (σ, κ): obtained through four‑probe resistance measurements and thermal conductance.
• Performance evaluation: measure power output and efficiency under ΔT in targeted ranges.
• Reliability tests: assess performance under thermal cycling to evaluate mechanical and electrical stability over time.

Innovation & Impact

• Fully CMOS/SOI‑based process enables integration with microelectronics and micro‑sensor systems.
• Nanostructured ultrathin Si reduces κ significantly, without sacrificing σ, enabling improved power factor and effective ZT in Si systems.
• Use of abundant, non‑toxic silicon provides cost advantage over Bi₂Te₃ or PbTe materials.
• Geometry optimization (e.g. corrugations, high-density arrays) maximizes thermocouple density and power output per area.

Potential Applications

• Integrated energy harvesting modules compatible with on‑chip deployment.
• Recovery of heat from microelectronic components or equipment.
• Self‑powered IoT/wearable sensors using ambient or body heat.

Master’s degree in Physics, nanoscience and nanotechnology, Electronics/IT Engineering (or similar);

Scientific ambition and enthusiasm, research-oriented attitude, capable of taking initiatives and with a solid problem-solving attitude; Ability to work in an interdisciplinary team, w/ good spoken and written English.

MicroEnergy Sources and Sensor Integration Group (MESSI): MESSI develops micro‑energy and smart sensing devices to tackle long‑term challenges like “Healthier Citizens” and “Net Zero Human Impact.” The group explores environmental energy harvesting (thermoelectricity) and energy generation/storage using micro‑fuel cells and biodegradable batteries, along with advanced sensor systems. A key focus is micro‑integrating energy sources and sensors into autonomous, self‑powered platforms by leveraging standard silicon technologies, rapid prototyping, and additive manufacturing.

Thermal Properties of Nanoscale Materials group (GTNaM): Affiliated also with ICN2: studies thermal properties of disordered and nanoscale materials, especially ultrathin films and low‑dimensional solids. They employ nanocalorimetry to investigate phase transitions in ultrathin films and 2D materials, often collaborating on size‑dependent effects. They also research nanoscale heat transport mechanisms involving phonons, electrons and photons to design thermoelectric harvesters and thermal sensors.