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Bonded SOI and C-SOI® wafers support high-precision medical MEMS

Insights, News+12/9/2025
Okmetic+About Okmetic+News & insights+Bonded SOI and C-SOI® wafers support high-precision medical MEMS

Medical MEMS devices require extreme precision, compact size, low power consumption, and long-term reliability. Okmetic’s Bonded SOI and Cavity SOI (C-SOI®) wafers meet these demands by providing an advanced, electrically isolated platform for high-performance sensing and efficient device integration. C-SOI® takes these benefits further with built-in cavities that also streamline production, improve yield and reduce device manufacturer’s processing steps.

These characteristics make Bonded SOI wafers with or without cavities ideal platforms for a wide range of medical MEMS devices such as fluid delivery devices, pressure sensors, accelerometers, temperature sensors, bio sensors, flow sensors, implantable sensors and ultrasonic transducers (PMUTs and CMUTs).

BSOI and E-SOI® support precision and integration

Okmetic’s Silicon-On-Insulator (SOI) wafers are manufactured by bonding together two silicon wafers with a thin insulating oxide layer in between. Sensing elements are typically built on the device layer. The buried oxide (BOX) layer provides electrical insulation and serves as an etch-stop or sacrificial layer during MEMS manufacturing.

BSOI and E-SOI® wafers offer the mechanical strength and long-term stability needed for medical environments. The SOI structure supports high precision, low power consumption, compact device dimensions, and a high degree of integration. Multiple sensing or actuation elements can operate reliably on a single chip thanks to the BOX layer enabling electrical isolation and reduced parasitic capacitance.

Enhanced SOI (E-SOI®) wafers take precision further with exceptional device layer thickness uniformity (±0.1 μm for 200 mm). This tight control ensures consistent performance across high-precision MEMS, making E-SOI® ideal for advanced medical applications.

Bonded SOI wafer benefits over SSP and DSP wafers:

  • Miniaturization and integration: Enables compact, and precise MEMS structures with multiple functionalities on a single wafer. Possibility to use thicker device layers when required for specific medical MEMS designs.
  • Mechanical robustness and reliability: Strong structure supports long-term use in demanding medical environments and across temperature variations.
  • Low power consumption: Reduced parasitic capacitance leads to lower power requirements, essential for battery-operated implantable devices.
  • Cost efficiency: Lowers manufacturing costs by decreasing component count and simplifying production processes.

C-SOI® wafers with built-in cavities add design freedom and streamline production

Cavity Silicon-On-Insulator (C-SOI®) wafers are bonded SOI wafers with sealed cavities embedded in the wafer structure. These embedded cavities enable more advanced device architectures than traditional bonded SOI wafers, supporting both MEMS sensors and MEMS-based fluid delivery devices. With cavity and trench-based structures, C-SOI® wafers can form integrated chambers or channels, and the built-in cavities allow movable parts such as membranes or sensors to be incorporated directly into the substrate. Because the cavities are created during wafer manufacturing, C-SOI® acts like a partially built device, streamlining MEMS processing, reducing production steps, and accelerating development while lowering cost.

Okmetic’s EC-SOI wafers combine the ultra-uniform device layer of E-SOI® with the built-in cavity structures of C-SOI®, creating a high-precision platform for advanced medical MEMS devices. A recent collaboration with VTT Technical Research Centre of Finland demonstrates how these wafers enhance performance of ultrasonic transducers.

C-SOI® wafer benefits:

  • Integrated cavities for MEMS structure: Enables incorporation of movable parts like membranes and sensors directly into the wafer, allowing for complex designs.
  • Reduced production complexity and cost efficiency: Minimizes additional production steps and the number of separate components, enhancing reliability and lowering production costs.
  • Superior performance and sensitivity: Finetuned cavities improve overall device sensitivity and performance in high-precision medical diagnostics.
  • Improved reliability and signal integrity: Reduces the likelihood of mechanical failure and minimizes noise interference, ensuring consistent performance and accurate detection.
  • Compact design with higher level of integration: Enables smaller devices with multiple functions.