Automated Spray Deposition of Liquid Metal: Process Assessment Towards Scalability and Reliability for Stretchable Electronics

Liquid metal stretchable electronics (LMSE) offer remarkable stretchability, softness, and self-healing properties, making them ideal for smart wearables and soft robotics. A key fabrication method involves spray deposition of LM into patterned structures. However, reliance on manual airbrush techniques has hindered understanding of how spray parameters impact LM deposition, limiting scalability and reliability. This work addresses these challenges by using an innovative automated spray coater (ASC), which provides precise control over deposition. For the first time, the ASC enables a systematic investigation of how spray parameters—such as flow rate, pressure, and spraying distance—affect LMSE properties like reliability, uniformity, and hysteresis. We find that rougher coatings improve yield (nearly 100\%), but compromise long-term reliability. Additionally, finer linewidth patterns (0.25 mm) fail earlier in cyclic testing and show reduced self-healing capabilities compared to wider lines ($>0.5 mm$). The ASC's capabilities are demonstrated through the fabrication of LMSE devices, including a 16-LED array and a large wearable strain sensor (70 × 150 mm) for human motion capture. This work provides crucial insights into LM deposition and highlights relevant applications, advancing the development of scalable and reliable stretchable electronics.