Hands-on fabrication of 2D material field-effect transistors for the classroom

The work presents a classroom experiment for building and testing field-effect transistors from two-dimensional semiconductors without access to a cleanroom or semiconductor fabrication equipment. It addresses a teaching gap: conventional transistor fabrication requires specialized processing, while many simpler ionic-gating demonstrations depend on custom-made electrolytes or careful handling. The proposed alternative uses commercially available hydrogel conductor pads developed for TENS devices, prefabricated thin-film interdigitated electrodes, and mechanically exfoliated MoS₂ flakes as the transistor channel. The materials and straightforward assembly are intended to make device fabrication feasible in a standard teaching laboratory.

The hydrogel acts as an ionic gate, enabling strong carrier modulation at low voltages. Its capacitance is characterized with a resistor-capacitor measurement, using the charging response to estimate capacitance; measurements across different sample areas show the expected area dependence, while the areal capacitance varies with measurement frequency. Representative transistor measurements demonstrate that gate voltage modulates channel conductance and reveal characteristic behavior of ionic-gated devices. The experiment is designed for undergraduate and early graduate courses, connecting electronics and solid-state physics concepts to fabrication and electrical characterization. Its central contribution is a practical, low-infrastructure route for students to make and analyze a working van der Waals transistor without custom electrolyte preparation, vacuum deposition, or foundry access.