Springer Berlin Heidelberg

Design and numerical analysis of a MEMS capacitive pressure sensor with engineered serpentine springs for intraocular pressure monitoring - Microsystem Technologies

This paper presents the design and numerical investigation of a capacitive MEMS pressure sensor specifically engineered for intraocular pressure (IOP) monitoring over the physiological range of 0–8 kPa (0–60 mmHg). In ophthalmic applications, strict size constraints are imposed to avoid visual field obstruction when the sensor is integrated onto ocular lenses or implantable platforms. However, reducing the sensor footprint particularly limiting the diaphragm radius to 100 $$\:\:{\upmu\:}\text{m}$$ inherently degrades pressure sensitivity and poses a major design challenge. The key novelty of this work lies in an application-driven structural design approach, in which an asymmetric arm serpentine suspension is engineered to overcome the inherent sensitivity loss associated with aggressive miniaturization required for intraocular pressure monitoring. A tunable geometric asymmetry parameter, defined as γ = L₁/L₂, is introduced to tailor the effective stiffness of the suspension and optimize electromechanical performance. Parametric studies on diaphragm thickness, electrode gap, and spring arm asymmetry are conducted to guide the final design. The optimized configuration features a 4 $$\:{\upmu\:}\text{m}$$ thick circular diaphragm suspended above a fixed bottom electrode with a 3 $$\:{\upmu\:}\text{m}$$ initial gap and a 0.1 $$\:{\upmu\:}\text{m}$$ silicon nitride dielectric layer to ensure electrical insulation and prevent pull-in instability. Finite element simulations show that the corresponding mechanical and capacitive sensitivities are 2.596 × 10⁻⁴ $$\:{\upmu\:}\text{m}$$ /Pa and 2.66 × 10⁻⁵ pF/Pa, respectively. Compared to a conventional symmetric configuration, the optimized asymmetric design (γ = 10) achieves a 1.21× improvement in mechanical sensitivity, a 1.72× enhancement in capacitive sensitivity, an approximately 82% reduction in geometric nonlinearity, and a 2.12× increase in the figure of merit. The proposed design is fully compatible with standard MEMS fabrication processes, making it a promising candidate for compact and reliable IOP monitoring applications.