Laser direct writing of Ga₂O₃/liquid metal-based flexible humidity sensors

Abstract

Flexible and wearable humidity sensors play a vital role in daily point-of-care diagnosis and noncontact human-machine interactions. However, achieving a facile and high-speed fabrication approach to realizing flexible humidity sensors remains a challenge. In this work, a wearable capacitive-type Ga 2 O 3 /liquid metal-based humidity sensor is demonstrated by a one-step laser direct writing technique. Owing to the photothermal effect of laser, the Ga 2 O 3 -wrapped liquid metal particles can be selectively sintered and converted from insulative to conductive traces with a resistivity of 0.19 Ω•cm, while the untreated regions serve as active sensing layers in response to moisture changes. Under 95% relative humidity, the humidity sensor displays a highly stable performance along with rapid response and recover time. Utilizing these superior properties, the Ga 2 O 3 /liquid metal-based humidity sensor is able to monitor human respiration rate, as well as skin moisture of the palm under different physiological states for healthcare monitoring.

Soft actuators based on the flexible MOF MIL-88B(Fe) with a fast response to various organic solvent vapours

“…Inspired by the easy fabrication of the LIG sensor, a LIG methanol sensor was fabricated by coating a mixture of MIL-88B and PVDF in DMF to the LIG surface. 51–54 Interestingly, although the coating was very thin and the solvent-driven deformation of the LIG was tiny to the naked eye (Fig. 7(D)), it was sensitive enough to methanol vapor that the introduction of 1 vol% methanol gas led to an approximately 400 Ohm decrease in the resistance.…”

Facile and Cost-Effective Fabrication of Highly Sensitive, Fast-Response Flexible Humidity Sensors Enabled by Laser-Induced Graphene

“…The importance of respiration for the human body is undeniable. It serves as an indicator of the body’s health status, making respiratory monitoring highly significant in the medical and healthcare fields. − The flexibility of the LIG humidity sensor allows it to be conformally attached to the inner wall of a plastic mask for respiratory monitoring as depicted in Figure a. In contrast, rigid MEMS sensors cannot be bent for such a conformal attachment.…”

Current On-Skin Flexible Sensors, Materials, Manufacturing Approaches, and Study Trends for Health Monitoring: A Review

“…Cui et al 167 developed a wearable capacitive humidity sensor based on a polyimide substrate + liquid-metal gallium(III) oxide system (Ga 2 O 3 /LM), manufactured via a laser direct writing technique, for respiration rate and skin moisture monitoring applications. The sensor exhibited a resistivity of 0.19 Ω cm, at a laser fluence above 6.8 J/cm 2 and a maximum capacitance change of 136.3% in the 30−95% RH range, with an electrode width of 1.5 mm and a temperature of 20 °C, as well as a highly stable cycling stability, where no significant degradation was observed at the end of 46 h of continuous use.…”