# Characterisation of Titanium-Oxide Thin Films for Efficient pH Sensing in Low-Power Electrochemical Systems

## TL;DR

This paper develops a low-power pH sensor using titanium-oxide thin films for use in cell culture and Organ-on-Chip devices.

## Contribution

The study introduces a low-temperature atomic layer deposition method for creating efficient pH-sensitive titanium-oxide layers.

## Key findings

- TiOx layers deposited via low-temperature atomic layer deposition showed high pH sensitivity (54.8–56.7 mV/pH).
- Low-temperature deposition outperformed sputtering and high-temperature methods for pH sensing.
- The sensor integrates with a low-power readout circuit for practical cell culture applications.

## Abstract

A compact electrochemical sensor module for pH detection was developed for potential integration into specialized devices used for live cell or tissue incubation, for applications in highly parallelized cell culture analysis, by incorporating Organ-on-Chip devices. This research focuses on the deposition, structural and chemical analysis, and functional characterization of different titanium-oxide layers with various compositions as potentially sensitive materials for pH sensing applications. The titanium-oxide layers were deposited using vacuum sputtering and atomic layer deposition at 100 °C and 300 °C, respectively. Transmission electron microscopy and X-ray photoelectron spectroscopy were utilized to determine the specific composition and structure of different titanium-oxide layers. These TiOx-functionalized electrodes were connected to the application-specific analog front-end chip of the low-power readout circuit for precise evaluation. The pH sensitivity of the differently modified electrodes, employing various TiOx materials, was evaluated using pH calibration solutions ranging from pH 6 to 8. Among the various deposition solutions, such as sputtering or high-temperature atomic layer deposition, the TiOx layer deposited using low-temperature atomic layer deposition proved more suitable for pH sensing applications, with a sensitivity of 54.8–56.7 mV/pH, which closely approximates the Nernstian response.