Towards a navigation grade Si-MEMS gyroscope

Northrop Grumman LITEF GmbH (NG LITEF) started the development of MEMS gyroscope chips with Deep Reactive Ion Etching (DRIE) in 2003. In parallel a 6 degree of freedom (DOF) micro electro mechanical system (MEMS) miniaturized inertial measurement unit (μIMU), based on these MEMS gyroscope chips and MEMS accelerometer chips also processed with DRIE, was designed. After successful transfer from early MEMS IMU prototypes to series production, NG LITEFs μIMU is available since many years with a specified 4°/h bias composite error at an angular random walk (ARW) of 0.15 °/√(h). Recently an European Technical Standard Order (ETSO) for the MEMS based Attitude Heading Reference System (AHRS) LCR-350B was received, so that NG LITEF is able to supply the first purely MEMS based AHRS worldwide to the avionic helicopter and fixed-wing market.The concept of NG LITEFs μIMU is based on three single gyroscope modules. In order to reduce the number of signal lines from the central signal processing board of the μIMU to the single modules, a MEMS gyro chip concept with only a few electrodes was selected. One of the major drawbacks of this approach is the high complexity of the electrical operation scheme, utilizing several auxiliary control loops multiplexed over the small number of electrodes.Due to the high complexity and the signal processing in the μIMU, a high level of computing power is required. In the last year NG LITEF has conducted research in order to improve the performance simply by optimizing the existing electrical operation scheme. As a result of these activities, ARW and bias error were reduced significantly without redesign of the MEMS gyroscope chips. Today, a single axis gyroscope performance of the order of 0.25 °/h bias model error over temperature, bias instability < 0.03 °/h and an ARW of below 0.025 °/√h can be presented.The paper covers the improvement in bias and ARW associated with the improved operation scheme as well as an outlook to the next MEMS gyro improvements and further MEMS gyro development activities planned at NG LITEF.