Development of a MEMS Multisensor Chip for Aerodynamic Pressure Measurements

Aerodynamic testing of various objects consists of pressure measurements at a multitude of points on aerodynamic surfaces or structural elements. Typically, the air pressure from the measurement points is transferred by flexible tubing to multichannel pressure sensing instruments. Existing instruments are usually built around an array of discrete pressure sensors, placed in the same housing together with a few discrete temperature sensors. However, such approach is limiting, especially regarding miniaturization, sensor matching and thermal coupling. In this work, we intend to overcome these limitations by proposing a novel MEMS multisensor chip. Although reports on chips with multiple pressure sensing elements exist in the literature, their concept and design are not suitable for this application. The silicon chip that we have developed has a monolithically integrated matrix of four piezoresistive MEMS pressure sensing elements, and two resistive temperature sensing elements. The thermal coupling between the integrated temperature and pressure sensing elements is much better than it can be between discrete sensors. This is important for temperature compensation of the pressure sensing elements. Another advantage is better matching of the pressure sensing elements characteristics, because they are fabricated in the same technological processes. After finishing the preliminary chip design, we performed computer simulations of mechanical influences that the pressure applied to one or more sensing elements can have on the whole multisensor chip structure. Subsequently, the final chip design was completed, and the first batch was fabricated. Technological processes included photolithography, thermal oxidation, diffusion, sputtering, micromachining (wet chemical etching), anodic bonding, and wafer dicing. Three silicon wafers were processed, each with 30 chips. Electrical tests have been carried out by using a probing station and a semiconductor parameter analyzer, and the full sensor characterization is in progress. Preliminary results indicate that the chip performs as expected.