The technology for the microfabrication of glass is gaining in importance because more and more glass substrates are currently being used to fabricate MEMS devices. Today, the glass material is strongly integrated into MEMS pressure sensors and optical MEMS as well as MEMS acceleration sensors and gyroscopes. Patterned wafers with cavities which can be obtained through etching are used to encapsulate the pressure sensor die. The encapsulation is done by using a wafer level packaging (WLP) approach.
Sensors have to a wide variety of applications in diverse fields. Significant portion of sensors is integrated in consumer electronic devices. Medical wearables such as fitness trackers, smartwatches is a new growing field where large variety of sensors such as pressure sensors, acceleration sensors, microphones, ambient light sensors find application. Sensors are also increasingly integrated into medical sector, being part of medical diagnostic equipment, dialysis and mechanical
ventilation equipment. Large market for sensor is an automotive sector, utilizing pressure sensors, acceleration sensors and others. Pressure sensors for example are performing a very critical functions in a car, such checking the pressure of critical fluids such as engine and transmission oil, tire pressure monitoring, airbag activation and seat occupancy detection to check seatbelt usage.
Pressure sensors have an extremely sensitive structure - very thin membrane that bends with applied pressure. This pressure is detected by piezo resistors on top of the membrane and converted into an electric signal. These fragile moving structures need to be protected from environment to ensure reliable function of a pressure sensor. Therefore, encapsulation is needed to hermetically seal the devices to protect them from harsh conditions. Encapsulation is often realized by bonding a capping wafer to sensor wafer via anodic bonding technology. Some sensors such as MEMS acceleration sensors, MEMS gyroscopes and MEMS pressure sensors require encapsulation under vacuum and hermetic sealing. Due to that all these sensors utilize glass for encapsulation.
Glass remains the preferred material as an encapsulation of sensors functioning in the demanding conditions. Glass offers chemical and temperature resistance necessary to withstand the harsh environment. Due to its high durability and chemical intentness, glass would be more suitable for areas exposed to extremely harmful conditions such as corrosion, where chemicals may react with other materials. The performance and reliability of sensors depends strongly on their robustness and durability in the long term. Superior durability and high reliability characteristics of glass remain extremely desirable for many applications such as automotive and medical field. Glass is widely used in pressure sensors specially for automotive sector. Glass is also a good option for optical sensors thank to its excellent optical transparency over the infrared and visible spectra.