Sensor Advances for Medical Applications

Low Pressure

The key to reaching the medical market is the development of sensors designed for very low pressure, which much of the industry classifies as under barometric pressure of 5psi.

In a conventional pressure sensor, a thinner diaphragm results in a device that can sense smaller amounts of pressure, but the trade-off is that it is much less linear. Therefore, overall performance (sensitivity and linearity) is not improved by simply making the diaphragm thinner. A major challenge in designing pressure sensors is to simultaneously make the linearity curve steeper and extend its linear range.

One solution for an ultra-sensitive pressure sensor is a thin boss structure created using silicon micromachining. Broadly speaking, the center boss is etched away to a thickness that is substantially smaller than the thickness of the substrate. By reducing the relative size of the boss, the device becomes less sensitive to gravitational forces, making it more robust. With the thin boss it is possible to obtain higher sensitivity while maintaining good linearity. Manufacturing the thin-boss structure is compatible with typical bulk micromachining processes, resulting in minimal cost increase.

Development of Low-Pressure Sensors

Technology Enablers

  • New sensitive MEMS-based boss structures: pressure ranges as low as 0.15psi
  • Varied boss designs allow lower pressure ranges to be achieved.
Mechanical stress concentrated at the piezo-resistor positions

Size reduction

One of the most important advances for medical applications is size reduction. Low pressure sensors can be used in invasive or external applications, but size will be an issue since much of the equipment and tools need to be either inserted or used by hand (for delicate surgery, for example).

SMI has achieved significant size reductions as a result of the implementation of process enhancements and continuous quality improvements, and as new MEMS-specific tools have been developed. SMI uses an Alcatel DRIE machine that provides deep, crisp and smooth cavity walls for high performance.

Development of Ultra-Small Sensors

Technology Enablers

  • Highly stable MEMS processes
  • New tools and procedures:
    • Deep reactive ion etching (DRIE)
    • Silicon on Insulator (SOI)
    • Expanded materials knowledge
    • Improved failure analysis
  • Quality programs and certifications
    • ISO: 9001
    • ISO/TS16949 (automotive industry standards)

Applications

  • Absolute pressure measurement inside the body (animal use only)
  • Next-generation catheter pressure sensors
  • Handheld units for delicate surgery (e.g. ocular, brain, cardiac, dental)

On-chip processing

Selected SMI pressure sensors are integrated, offering calibration, compensation, amplification, EEPROM and signal processing. The integration occurs via post-processing.

By virtue of their integration these smart single-chip sensors can help OEMs cut costs and cut down on PCB real estate.

Integration of On-Chip Signal Processing

Technology Enablers

  • Advanced CMOS
  • Continuous quality improvement

Benefits

  • Application-ready for displays, diagnostics, due to on-chip calibration, temperature compensation, amplification, and signal conditioning
  • High accuracy and lower cost

Applications

  • Anesthesia
  • Respiration monitoring
  • Sleep apnea

Harsh Media Pressure Sensing

SMI’s media resistant pressure sensor die offer the ability to stand up to repeat exposure to harsh environments, including fluids, gases and humidity. Many suppliers of harsh environment sensors opted to create transducers by encasing them in steel, which at one point was the only option. OEMs learned to live with it, but the advent of SMI’s smaller media harsh die offers system designers new options and business opportunities. SMI’s sensor circuitry is protected by the application of a layer of glass across the top of the die while providing a backside entry point for the media.

Harsh Environment Pressure Sensing

Technology Enablers

  • Bonding techniques

Benefits

  • Allows biofluid and additional chemical compatibility

Applications

  • Excess fluid extraction
  • Surgery waste fluid evacuation

Small Outline Packaging

A small-outline integrated circuit (SOIC) is an IC package that occupies an area about 30 - 50% less than an equivalent dual inline package, with a typical thickness that is 70% less. They are generally available in the same pinouts as their Dual inline package (DIP) counterparts. The DIP packages have hit real estate barriers as the lead count has increased in more complex chips

Small Outline Packaging: SO-8, SO-16

Technology Enablers

  • Smaller die

Benefits

  • Space savings

Applications

  • Portable medical electronics

Old Style TO-5 and TO-8 Packaging
Sensoren_SOIC8Sensoren_SOIC16_1
SO-8 and SO-16 Packages

For more information contact SMI sales at sales@si-micro.com.