This paper presents the design and fabrication method to render a silicon-on-insulator (SOI)-based pMUT array bendable. The proposed method can be applied to silicon-based pMUT arrays with different acoustical specifications. A bendable array based on the proposed method is highly conformal to the target structure. The bendable structure is made out of several silicon islands containing a pMUT array and are connected to each other by silicon springs. The silicon springs are realized by deep reactive ion etching (DRIE) that was also used to create the pMUT membranes. The fabrication process requires one additional photomask step compared to a process that realizes only pMUTs. Since the pMUT arrays are fabricated on silicon islands with the thickness of the entire SOI wafer, therefore their performance is not compromised. As a case study, a bendable array was designed and fabricated to be wrapped around a 5x5x5 mm³ 3D printed cube. Therefore, each bendable array has 6 islands with a dimension of 3x3 mm² including 3x3 pMUT array, of which each pMUT has a diameter of 410 μm and a thickness of 6 μm with a 1 μm Lead Zirconate Titanate (PZT) layer as the piezoelectric material. The silicon springs in between each island have a spring constant of 2.3 (N/m) in their folding direction. This compliant structure enables a 90° bending with a bending radius of 1 mm. The pMUT elements in the array resulted in a displacement response of 2.1 μm/V and a Q-factor of 104 at 426 kHz, when all arrays were excited all together. [2019-0224]

Deep wet etching of borosilicate glass using an anodically

We report the design and implementation of a unique, wafer sized stretchable and bendable monolithic silicon matrix structure. The achieved stretchability not only allows for one directional folding, but is capable of bending in two directions simultaneously, which is required to conform the structure to complex shapes such as spheres, tori, hyperboloids or a combination of them. Moreover, it also enables dynamic mechanical deformation of the structure to cope with a moving environment, e.g. the wall of the heart muscle. The minimal measured bending radius is 8 mm, which is 20% smaller than the current state of art. Furthermore, a new fabrication process is proposed that enables the use of common wafers. This enables a broader and more accessible applicability compared to earlier work, which is based on non-standard wafers, or the more expensive SOI wafers. The technique can lead to a revolutionary potential of applications, especially in the medical field, by enabling complex silicon monitoring systems to be linked to organs without hindering them.

We report the design and implementation of a unique, wafer sized stretchable and bendable monolithic silicon matrix structure. The achieved stretchability allows for simultaneous omnidirectional folding, required to conform the structure to complex curved 3D surfaces. Moreover, it also enables dynamic mechanical deformation of the structure to cope with a moving environment, like e.g., the wall of the heart muscle. Due to the nature of the fabrication process, normal silicon wafer processing can be performed prior to rendering it stretchable. This is first demonstrated by the fabrication of two metal layers on top of silicon, which act as the electrical interconnects of a final flexible and stretchable LED-matrix. Currently, the possibility to postprocess an existing commercial CMOS process is investigated. This would lead to a revolutionary potential of new applications, especially in the medical field, by enabling complex silicon monitoring systems to be linked to organs without hindering them.