3D Nanofabrication and Integration of Various Metal Oxides

Microsystems can achieve higher performance, smaller sizes, and lower power consumption through integrating three-dimensional (3D) functional structures of various metal oxides. However, the nanomanufacturing and heterogeneous integration of 3D functional metal oxides still face long-standing challenges. Currently, the mainstream 3D manufacturing techniques of metal oxide structures can be classified into two methods including particle-loaded bonding and femtosecond laser direct writing (FLDW). Particle-loaded bonding technology utilizes material's jetting or extrusion to achieve the 3D printing and heterogeneous integration of various kinds of metal oxides. However, its manufacturing resolution (&gt;10 μm) and quality (high roughness, low stiffness) are difficult to meet the application requirements of integrated microsystems. On the other hand, although the FLDW technology has nearly unrestricted 3D design freedom at the nanometer resolution, the 3D metal oxide structures manufactured by this technology commonly suffer from serious shape distortions, limited material applicability, and difficulties in heterogeneous integration.<br/>To address the above issues, we propose a method for 3D nano-printing and heterogeneous integration of various kinds of metal oxides by FLDW the water-soluble resin of metal ion-coupled coordination. This method has the following three main advantages: 1) The mechanism of mutual promotion between acrylic acid and 1-vinylimidazole in coupled coordination with metal ions has been proposed, which breaks through the concentration limit of metal ions in the 3D structure manufactured by traditional methods, increasing the metal ion content to 30.5% in the 3D structure, thereby significantly reducing the degree of morphological distortion. 2) The resin for FLDW is designed to be water-soluble, which may potentially extend this method to the processing of oxide of all water-soluble metal elements. 3) Sequential 3D printing according to the priority of metal activity enables the 3D heterogeneous integration of various functional metal oxides. The successful design of this printing method enables us to manufacture 3D nanostructures and heterogeneous integrated structures of various types of metal oxides, including MnO₂, Cr₂O₃, ZnO, NiO, and Co₃O₄. Furthermore, we demonstrate a high-sensitivity 3D ZnO micro-integrated sensor with a sensitivity of up to 1.113 million in a 200 ppm NO₂ environment, which is much larger than the sensitivity of the 2D device. Therefore, this printing method expands our capability to achieve the 3D manufacturing and integration of metal oxides at the nanoscale and demonstrate its significant application potential in the field of integrated sensing devices, integrated medical endoscopes, nanogenerators, and other 3D microsystem applications.