Handwritten Oxide Electronics on Paper

The present work reports on the handwriting of electronic circuits on paper based on the deposition of an inorganic oxide semiconductor, exploiting the pen‐on‐paper (PoP) approach. The method relies on the use of a parallel metal plate pen, well known from calligraphy applications, which permits controlled deposition of a continuous zinc oxide (ZnO) dual‐phase layer on conventional printing paper. The hand‐drawn ZnO film exhibits a continuous and uniform surface with a thickness of roughly 1.5 µm, allowing the application as active layer for UV sensors and field effect transistors on paper. Photocurrent generated from the UV radiation reaches values up to 3.4 mA cm⁻² with switching times on the order of few seconds. The final written paper transistors, where paper plays simultaneously the role of substrate and dielectric, reaches On/Off current ratios (I_On/I_Off) of about two orders of magnitude and field effect mobility close to 5 × 10⁻³ cm² V⁻¹ s⁻¹. As a final proof‐of‐concept a common source amplifier showing clear inverting characteristics is fabricated using a PoP written driving ZnO‐based transistor and a pencil‐drawn track as the load resistance.