# A Flexible and Thermally Uniform TiO2/Ag/SiO2 Transparent Heater for Skin-Integrated Applications

## TL;DR

A new transparent heater made of TiO2, Ag, and SiO2 is developed for wearable applications that can safely and uniformly heat skin.

## Contribution

A TiO2/Ag/SiO2 transparent heater is introduced with high optical transparency, mechanical compliance, and thermal uniformity for skin-integrated use.

## Key findings

- The heater achieves 86.6% visible-light transmittance and 7.7 Ω/sq sheet resistance for low-voltage operation.
- It provides rapid and uniform heating with no hot spots and stable performance under bending.
- On-skin testing showed conformal contact and uniform heating at 50–70 °C during motion.

## Abstract

Transparent heaters intended for skin-contacting applications must simultaneously satisfy optical transparency, mechanical compliance, thermal uniformity, and operational safety under biologically relevant temperature ranges. Here, we evaluate the applicability of a TiO2/Ag/SiO2 (TAS) dielectric–metal–dielectric transparent heater as a functional biomaterial platform for wearable and skin-integrated thermal systems. By systematically optimizing each layer thickness of the TAS structure, the heater achieves high visible-light transmittance (average of 86.6%) together with low sheet resistance on the order of 7.7 Ω/sq for low-voltage operation. The TAS heater demonstrates rapid and reproducible Joule-heating behavior, showing fast thermal response with short thermal time constants and spatially homogeneous temperature distributions without localized hot spots. Stable electrothermal performance is maintained under repeated on/off cycling and during cyclic mechanical bending down to small radii, confirming excellent mechanical stability under repeated bending relevant to wearable applications. Importantly, direct on-skin evaluations conducted by attaching the device to a human elbow reveal conformal contact, uniform heating at therapeutically relevant temperatures (50–70 °C), and stable operation under dynamic bending and extension. The absence of thermal inhomogeneity during motion highlights the intrinsic stability of the TAS architecture for skin-interfaced use. Given the high optical visibility, mechanical compliance, thermal uniformity, and electrothermal stability, the proposed TAS architecture represents a promising functional biomaterial platform for wearable thermotherapy, skin-mounted healthcare devices, and human-interactive thermal systems operating under continuous mechanical deformation and direct skin contact.