Laser direct writing Ga2O3 liquid metal based flexible humidity sensor

Recent research into emerging flexible humidity sensors has led to significant advances in advanced manufacturing methods as well as innovative applications including human health detection, plant health management and contactless human-machine interfaces. Capacitive humidity sensors are widely concerned because of their reliable humidity sensing performance, low power consumption and simple structure design. Generally, the performance of capacitive humidity sensors is closely related to the dielectric constant of the functional material between the sensor electrodes.

So far, various active materials have been studied as flexible capacitive humidity sensors, such as carbon materials, metal oxides, metal sulfides and polymers. Similarly, they usually have a large exposed surface area and an abundance of active sites to interact with water molecules. Ga 2 O 3, as a potential metal oxide with high exposure hydrophilic groups, has been used as an active material for capacitive humidity sensors.

The traditional preparation techniques of Ga 2 O 3 base humidity sensor mainly include chemical vapor deposition, heat treatment and hydrothermal method. However, these methods usually require high annealing temperatures, complex manufacturing processes, and multiple material systems, which hinder their practical application.

Digital laser direct writing is a fast, environmentally friendly manufacturing method for generating functional micro/nano structures or directly creating high-precision sensitive nanomaterials. A variety of innovative flexible sensors have been demonstrated, such as physical, chemical and physiological sensors, based on the interaction of laser with matter, by judiciously selecting the appropriate laser processing parameters.

Typical strategies typically rely on laser writing directly into the electrode and then depositing a water-sensitive nanomaterial, such as a carbon or metal sulfide-based material, on top of the electrode. However, this leads to multiple complex processes. Therefore, there is still a need for a simple and easy way to develop thin-film based humidity sensors.

In this new work, published in Opto-Electronic Advances, a wearable capacitive Ga 2 O 3 / liquid metal humidity sensor is demonstrated using single-step laser direct writing technology. Due to the photothermal effect of the laser, Ga 2 O 3 coated liquid metal nanoparticles can be selectively sintered and converted from insulated wire to conductive wire with a resistivity of 0.19 Ω·cm, while the untreated region is used as an active sensing layer in response to moisture changes.

Humidity sensors show highly stable performance and fast response and recovery times at 95% relative humidity. Using these superior features, Ga 2 O 3 / Liquid metal-based humidity sensors can monitor human respiration rates, as well as the skin moisture of the palm under different physiological conditions for healthcare monitoring.

Source: Laser Net