Capacitive Sensing Technology for Industrial Robots

Designing a Calibration Wafer

This client is a global industrial manufacturing company that designs machines that fabricate silicon wafers. A silicon wafer is a thin slice of semiconductor, and this client offers a wide range of wafer processing capabilities to deliver products and technologies that help create transistors, interconnects, advanced memory, and packaging structures.

Second Order Effects was engaged to create a “calibration wafer” that would ride through the fabrication machine, measure the distance between itself and another object, and report it back in real-time, calibrating the production line and ensuring high yield.

Requirements to be met by SOE’s calibration wafer:

  • be built with the exact size and weight specifications as the silicon wafers that the machines typically process.
  • be able to survive extreme environments of the manufacturing process, which included temperatures up to 150 degrees Celsius and vacuum up to 1m torr
  • detect distances between 100 μm to 10mm with a resolution of 5 μm

SOE selected a promising capacitive sensor driver chip that could meet performance specifications and nearly meet accuracy over temperature specifications. To address temperature risks, SOE developed a prototype test setup that could generate a known variable gap to be detected. The gap’s accuracy over exposure temperature was detected and a methodology of compensating for temperature drift in the wide range of 0-150 degree celsius in a repeatable fashion was developed


Prototype test set up featuring a variable temperature output heat gun, capacitive sensor IC development board, and micrometer testing device.

A: Variable temperature output heat gun.

B: Capacitive Sensor IC development board

C: Prototype Capacitive Sensing test device with micrometer

Zoomed view of the gap between two metal boards with the analog measurements of capacitive system's characterized drift over temperature in the background.

D: Analog measurements of Capacitive sensor output monitored with temperature sensors to characterize distance measurement drift over temperature.

E: Metal gap distance sensed by Capacitive System


SOE designed, build, characterized drift over temperature, and shipped the wafer to the client. Although the wafer never made it into a product, the capacitive sensing technology developed here will be applied to our client’s robot proximity sensors going forward.