Langasite Bonding via High Temperature for Fabricating Sealed Microcavity of Pressure Sensors

Abstract

We proposed a novel Langasite (LGS) bonding method only using high temperature to solve the manufacturing difficulty of the sealed microcavity of pressure sensors. The optimal bonding parameters by comparative experiments were defined as 1350 °C for 3 h. Due to simple experimental conditions, low experimental cost, and be suitable for bonding wafers with various sizes, the method is convenient for popularization and mass-production, thus promoting the development of surface acoustic wave (SAW) devices at high temperatures. Simultaneously, an intact microcavity was observed by scanning electron microscopy, and a tight and void-free bonding interface with a transition layer thickness of 2.2 nm was confirmed via transmission electron microscopy. The results of tensile and leakage experiments indicated that the bonded wafer with the sealed microcavity exhibited a high bonding strength of 4.02 MPa and excellent seal performance. Compared to the original wafer, the piezoelectric constant of the LGS bonded wafer had a reduction of only 4.43%. The above characteristics show that the sealed microcavity prepared by this method satisfies the conditions for fabricating the LGS SAW pressure sensors. Additionally, based on the bonding interface characterizations, the mechanism of LGS bonding has been investigated for the first time.

Growth of Single-Crystalline GaN Films on Ga-Free Langasite-Type Crystals by Metal–Organic Chemical Vapor Deposition

“…Figure a shows the photograph of the CNAS substrate after the growth of GaN films by MOCVD for 1.5 h. The surface is smooth, and the color turns to be deep dark, which is influenced by the high-temperature growth atmosphere . The surface morphology of the GaN film grown on CNAS was investigated via SEM and AFM.…”

“…Figure 4a shows the photograph of the CNAS substrate after the growth of GaN films by MOCVD for 1.5 h. The surface is smooth, and the color turns to be deep dark, which is influenced by the high-temperature growth atmosphere. 18 The surface morphology of the GaN film grown on CNAS was investigated via SEM and AFM. In Figure 4b, the plane-view SEM image indicates that the surface of the GaN film is smooth and continuous without cracks, yet several pits are observed.…”

Characterization of photoelastic materials by Mach–Zehnder interferometry: Application to trigonal calcium galogermanate (CGG) crystals

“…Calcium galogermanate crystals Ca 3 Ga 2 Ge 4 O 14 (CGG) belong to A 3 BC 3 D 2 О 14 group of inorganic crystalline materials with trigonal symmetry, i.e., the family of langasite (LGS) crystals 1,2 intensively studied in recent years due to their high piezoelectric, photoelastic, acousto-optic, and nonlinear optical efficiency making them promising for acousto-electronic and optoelectronic applications. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Langasite La 3 Ga 5 SiO 14 was one of the first grown crystals with such a structure whereas extensive studies of other crystals of this group allow us to draw relevant conclusions about the impact of cationic substitution both on the crystal structure and related physical properties. 1,[3][4][5] By changing the chemical composition, these studies are aimed at improving the physical characteristics of crystalline materials for relevant applications.…”

“…14 All this makes the crystals of the langasite group unique and suitable for wide range of applications in acousto-and optoelectronic devices. [14][15][16][17][18] Optical characterization of LGS type crystals has been concentrated basically on luminescent, refractive, spectroscopic, 9,19,20 photoelastic, and acousto-optic [21][22][23] properties in recent years. Derived in these studies, photoelastic and acousto-optic characteristics evidently indicate that LGS and CTGS crystals represent efficient acousto-optic materials suitable for light modulation in the ultraviolet spectral region.…”