From TPMS systems for tires and monitoring powertrain functions to airbag and seatbelt activation, pressure sensors in the automotive industry perform a wide range of tasks that enable performance and safety.
The field of medical science increasingly relies on pressure sensors to improve processes such as minimally invasive surgery (MIS), artery detection techniques, the development of robotic prosthetics, and improved biological analysis of patients.
Technology such as smartphones and smart watches are part of a market that demands ever-smaller, lighter and more sensitive pressure sensors. This market will develop further, with more functions needing new sensors while driving costs down.
Industrial sensors convert pressure into analogue or digital signals that accurately measure stock or control levels of industrial gas and liquids. These pressure sensors need to maintain outstanding performance in the harshest chemical and thermal environments.
Consistent performance of electronics in aviation depends on reliable pressure sensors. Over the lifetime of an aircraft, robust and reliable glass packaging will protect and optimize a sensor’s performance in intensely hostile conditions.
3. Principle of anodic bonding
Central to the accuracy, reliability and longevity of a high performance pressure sensor is the join between the borosilicate glass packaging component and the functional silicon unit. The bond is formed electrochemically at wafer level by an anodic bonding process at a temperature of about 400 °C and voltage up to 2,000 V, uniting the chemical components in the glass and silicon. This bond needs to be strong and stable, contributing to the high electrical, thermal and chemical resistance demanded from the die packaging solution.
Advantages of glass substrates and wafers
Prof. Dr.-Ing. Roy Knechtel explains the importance of effective packaging for MEMS-based pressure sensors and why glass is the ideal material.
The key markets of MEMS* based pressure sensors are automotive, medical, industry and consumer applications. Today’s and future requirements differ from application to application within these segments. In the automotive, medical and industrial sectors, product developers focus on improving precision, long-term stability and robustness – also taking harsh environments into account.
For high-volume consumer applications, increasing demand for miniaturization at low cost is the challenge.
(*Micro Electro Mechanical System)
The packaging of the mechanical stress-sensitive silicon MEMS dies is highly important as it co-determines the overall performance of the system. For the so-called first-level-packaging there are three main tasks:
- providing stress decoupling and electronical isolation to the final module and system-level package,
- enabling a hermetically sealed reference pressure and
- providing additional protection e.g. to harsh media.
With the increasing need for improved pressure sensor system performance, glass packaging solutions are facing ongoing challenges. Smaller dies allowing higher number of dies per wafer. This require tighter tolerances in hole positioning and diameter of structured pressure sensor pedestal wafers. Best to realize in glass that is as thin as possible, to reduce the overall device thickness but keeping the stress isolation feature.
With ultra high-precision FLEXINTY® portfolio of structured glass, in combination with MEMpax®, a polish- & surface defect free ultra-thin “sister” material to the well-known BOROFLOAT® 33, a high-performance glass-based solution is now available to meet the future demands of the pressure sensor market.