Using its own spherical semiconductor fabrication methodology, Ball Semiconductor has demonstrated a prototype of a new type of micromachined sensor that can be used for measuring tilt angle, impact and vibration.
Dubbed the Ball omni-directional clinometer, the sensor was jointly designed with Tohoku University and the circuit to control it was developed in conjunction with Tokimec.
The clinometer itself is made from a 1mm diameter silicon ball core, which is surrounded by a special shell structure. On the inner wall of the shell, there are three pair of electrodes for measurement of movement in three axes as well as one common electrode. The core ball moves freely inside the shell. And by measuring the capacitance between the electrodes, the tilting angle along three axes can be determined.
The first step in making a Ball integrated circuit is the fabrication of single crystal spheres. Poly-crystal granules are first sorted by weight and/or size to provide the appropriate raw material for the 1-mm single crystal spheres.
These granules are then preheated in a furnace and melted by a high-energy plasma source. The melted granules are then dropped through a long tube where they are cooled.
The heating and cooling rates are adjusted such that the granules become single-crystal spheres. Substrate doping is achieved by introducing appropriate dopants either during the heating or cooling cycle.
The single crystals are then polished to a mirror-like finish with no surface deformities by both chemical and mechanical means.
BSI expects that its sensors will used as ‘gesture interpretation sensors’ for wearable computers, PDA’s and cell phones interface.
The company expects that sensors based on the new technology will be available by the end of the year.