Hydrophilic Direct Bonding of MgO/MgO for High-Temperature MEMS Devices

Abstract

Single-crystalline magnesium oxide (MgO) is an attractive material of substrates for hightemperature devices and high-temperature superconducting films. However, it is difficult to achieve the direct bonding of MgO/MgO because of its high brittleness and hardness, as well as the weak bonding force between the crystal faces. In this paper, we presented a hydrophilic direct bonding method of MgO by using two-step surface activation and a high-temperature annealing process. The bonding strengths under different annealing temperatures, pressures and times were measured. A high bonding strength (∼7 MPa) and a fine bonding interface without any microcracks and voids were obtained after annealing at 1200 • C, 140 min and 4 MPa. The bonding interface was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The bonding mechanism of MgO/MgO was also clearly clarified. For the demo application, a MgO sealed cavity was formed by using the direct bonding method which is commonly used in the microelectromechanical systems (MEMS) devices for harsh environment applications. INDEX TERMS MgO single crystal, direct bonding, surface activation, high temperature annealing, bonding interface.

An LC Wireless Passive Pressure Sensor Based on Single-Crystal MgO MEMS Processing Technique for High Temperature Applications

“…Correspondingly, the thickness of the pressure-sensitive diaphragm was 126 μm. Then, direct bonding of the etched MgO and bare MgO (thickness of 400 μm) was performed, using a surface activation-assisted high-temperature annealing direct bonding method, as shown in Figure 2 f. According to our previous research on the bonding strength of MgO/MgO under different annealing conditions [ 33 ], the parameters of direct bonding for the sensor substrate were determined to be a pressure of 4 MPa, a temperature of 1300 °C, and a duration of 140 min. Then, the vacuum-sealed cavity was produced.…”

Periodic Al2O3 Nanohole Arrays on MgO (100) for a Low-Reflectivity External Cavity Fabry–Pérot Interferometer

“…As an optical glass with an extremely high melting point, MgO has become a new material in the field of ultrahigh-temperature optical devices. − MgO also has excellent mechanical properties and high thermal conductivity . MgO materials are also ideal carriers for optical coatings and functional films. ,− When the wavelength is in the c-band (center wavelength 1550 nm), we consulted the manual and tested that the overall transmittance of the MgO (100) wafer is around 86%, and the transmittance of the interface is 93%.…”

Highly Transparent Polycrystalline MgO via Spark Plasma Sintering

“…A growing interest in transparent ceramics for various optical components, laser materials, scintillators, and more is evident in recent years. , One of the promising materials for infrared (IR) window applications is magnesium oxide (MgO) due to its wide transmission range (300 nm to 6 μm) and excellent thermo-mechanical properties . In addition, MgO is used as an attractive alternative substrate material to sapphire and silicon for high-temperature microelectromechanical systems and as substrates for high-temperature superconductor applications. , …”

“…1,2 One of the promising materials for infrared (IR) window applications is magnesium oxide (MgO) due to its wide transmission range (300 nm to 6 μm) and excellent thermo-mechanical properties. 3 In addition, MgO is used as an attractive alternative substrate material to sapphire and silicon for high-temperature microelectromechanical systems 4 and as substrates for high-temperature superconductor applications. 5,6 Optically transparent ceramics in general and MgO in particular are conventionally produced by vacuum sintering, hot-pressing, and hot isostatic pressing at very high temperatures and/or prolonged sintering durations.…”