Integrated Tire Pressure Sensor
Original Publication Date: 2003-Aug-25
Included in the Prior Art Database: 2003-Aug-25
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An important aspect of the general safety of cars is the monitoring of the tire pressure. Today this is implemented by using two separate devices, a sensor for measuring the tire pressure and a unit for analyzing the data and sending it to the car's frame. This invention shows a way to combine the sensor and the analyzing component into one device by integrating the production of the sensor into a standard CMOS (Complementary Metal Oxide Semiconductor) fabrication process, thus achieving higher durability and reducing the production costs and the size of the device. In a BEOL (Back-End-Of-Line) process, the last two metal layers are shaped as two large plates of similar dimensions. The last layer is placed directly on top of the plate underneath and in the center of the upper plate a small hole is inserted. After the metal patterning of the upper plate is finished, an extra photo layer is used to partly etch away the inter-layer dielectrics through the hole in the top plate. This process has to be tuned to create a well defined cave in between the two plates. Finally, a standard terminal dielectrics deposition is applied. Since this passivation process has a poor ability to fill high aspect ratios or hidden cavities, the cave remains mainly empty. Due to the fact that the cave is now hermetically sealed, every environmental pressure change leads to a variation of the plate-to-plate distance and consequently to a change in the capacity. Therefore the measurement of the plate-to-plate capacity can be used to measure the pressure outside the chip.