Miniaturized Transformer Bridge Setup for Scanning Thermal Microscopy Applications

Scanning thermal microscopy (SThM) methods typically utilize the Wheatstone bridge for temperature readout. In this article, we present a small form-factor transformer bridge developed for investigating thermal properties through resistance change measurements. Compared to resistive bridges, this method allows galvanic separation between the system and sample, thereby enabling the measurement of biased samples. We present magnetic measurements of the nanocrystalline transformer core, including magnetization curve and permittivity, which are crucial for proper winding design. The characteristics of the fabricated transformers are presented, based on inductances and losses measurements. The response of the entire setup is assessed, and the equivalent circuits are discussed, which provides the system performance in terms of noise, sensitivity, and resolution. The voltage noise of the circuitry $1~\mu $ VRMS and thermal sensitivity of 5 mV/K yielded a theoretical limit of 0.6 mK for the temperature resolution. The proposed transformer bridge is intended for use in indirect thermal measurements in an in-house developed scanning thermal microscope.