Hermetic capacitive pressure sensors for biomedical applications

Abstract

Purpose This paper aims to purpose the new design and fabrication scheme of Touch Mode Capacitive Pressure Sensor (TMCPS), which can be used in a wireless integrated resistor, inductor and capacitor circuit for monitoring pressure in biomedical applications. Design/methodology/approach This study focuses on the design, simulation and fabrication of dynamic capacitors, based on surface micromachining using polysilicon or aluminum films as the top electrode, both structural materials are capped with a 1.5 μm-thick polyimide film. Findings The design of microstructures using a composite model fits perfectly the preset mechanical behavior. After the full fabrication, the dynamic capacitors show complete mechanical flexibility and stability. Originality/value The novelty of the method presented in this study includes two important aspects: first, the capacitors are designed as a planar cavity within a rigid frame, where two walls contain channels which allow for the etching of the sacrificial material. Second, the electromechanical structures are designed using a composite model that includes a polyimide film capping for a precise pressure sensing, which also protects the internal cavity and, at the same time, provides full biocompatibility.

Research on a capacitive MEMS pressure sensor based on through glass via

“…According to the different capacitance output characteristics caused by diaphragm deformation, it is divided into four regions: normal mode, transition mode, touch mode, and saturated mode. 18,19 The capacitive pressure sensor started to work in the normal mode with small deflection deformation. As the external pressure gradually increased, the diaphragm gradually deflected downward and the effective gap gradually decreased.…”

Design and Simulation of an Integrated Wireless Capacitive Sensors Array for Measuring Ventricular Pressure

“…In this approach, both plates are isolated by a double insulator, air/silicon oxide, allowing a dynamic variable capacitive sensor [47,53,54,55], as can be seen in the layout of Figure 5b. The 555 µm-side capacitor was mechanically designed in order to respond under the lower LV pressure regime, while the 300 μm-side capacitor was designed to get a response under the highest LV pressure regime.…”

“…The detection principle of the capacitive array is based on the relationship between the changes in capacitances for a given applied pressure [8,47,49,54]. In this case the total capacitance, at any time, is the sum of the individual capacitances associated at a given pressure, as follows:${\mathrm{C}}_{\mathrm{s}}=\frac{{\mathsf{\epsilon }}_0{\mathsf{\epsilon }}_{\mathrm{aire}}{\mathsf{\epsilon }}_{\mathrm{normald}1}{\mathrm{A}}_{\mathrm{touch}1}}{{\mathrm{W}}_{\max 1}{+\mathrm{sans-serif\epsilon }}_{\mathrm{normald}1}{\mathrm{W}}_{\max 1}}+\frac{{\mathsf{\epsilon }}_0{\mathsf{\epsilon }}_{\mathrm{aire}}{\mathsf{\epsilon }}_{\mathrm{normald}2}{\mathrm{A}}_{\mathrm{touch}2}}{{\mathrm{W}}_{\max 2}{+\mathrm{sans-serif\epsilon }}_{\mathrm{normald}2}{\mathrm{W}}_{\max 2}}$ where ε d is the dielectric constant of the insulating material, A Touch is the contact area of the diaphragm, W max is the separation distance between the parallel metal plates and the subscripts 1 and 2 stand for the first and second capacitive structure, respectively.…”

“…( b ) Flexible LC prototype implanted in a rabbit’s eye [45,46,47,48]. Reprinted from Microelectronic Engineering, Vol.159, Félix Gil Carrasco, Daniela Díaz Alonso, Luis Niño-de-Rivera, Biocompatibility and implant of a less invasive intraocular pressure sensor, Pages No.…”

“…The conception of the implantable capacitive array and the inductive coupling link are designed for accomplish practical, accurate, and real-time wireless pressure sensing. This novel design is supported by our previous work: (a) A magnetically coupled planar coils for wireless power transfer in intraocular pressure measurements [45]; (b) An aluminum based thin film technique for the fabrication of capacitive sensors [46,47], and (c) The implantation of an experimental LC prototype beneath the conjunctiva of a rabbit’s eye using a very simple surgery. The sensors array has the capability to adjust between the conjunctiva and the cornea without an aggressive invasive procedure; the LC array did not suffer rejection; tissue irritation disappears after three weeks; the prototype showed good stability, and the rabbit tolerated this implant during six months before its sacrifice [48].…”