The Study Of Anodic Bondable Low Temperature Co-fired Ceramics (LTCC) Materials

Silicon based MEMS（Micro-Electro-Mechanical System,MEMS）devices are widely used in consumer electronics,military and aerospace fields.LTCC（low temperature co-fired ceramics,LTCC）technology can realize the high-density encapsulation of electronic devices.The MEMS devices encapsulated with LTCC substrate can realize 3D packaging,greatly reducing its volume and weight.Therefore,the anodic bondable LTCC material directly affects its encapsulation and performance of MEMS devices.This thesis focusses on the high-density packaging of silicon-based devices.Composites of LABS glass+β-Al₂O₃ and LNABS glass-ceramics were designed and prepared for low temperature and voltage anodic bonding of Si-LTCC.The LNABS glass-ceramics were successfully anodic bonded to Si substrate under low temperature and low voltage.The anodic bonding mechanism of Si-LTCC at low temperature voltage was studied.A theoretical model of Si-LTCC anodic bonding with low temperature and voltage was established.The compatibilities of metal electrodes（Al and Ag）and LTCC tapes were studied.A MEMS pressure sensor was encapsulated with LNABS glass-ceramics.A micro-reactor for 2D SnSe nanosheets growth study was designed and fabricated with Si-LTCC anodic bonding technology.The main contents and results are listed as follows:1.The study of Li-Al-B-Si-O（LABS）glass andβ-Al₂O₃ compositesThe crystallization mechanism and kinetics of LABS glass were studied systematically.The studies of XRD and SEM of LABS glass-ceramics indicate that theβ-spodumene crystallizes in a two-dimensional growth mechanism.The main phase of LABS glass-ceramics is LiAlSi₂O₆ solid solution.The crystallization kinetic of LABS glass-ceramics is 59.9 kJ/mol,indicating lithium ions determine its crystallization.The sintering temperatures of LABS glass andβ-Al₂O₃ composites are below 900°C.The main phase of sintered composites is Li₂Al₂Si₃O₁₀ whenβ-Al₂O₃ content is lower than35%.However,the phases of composites areβ-Al₂O₃,Li₂Al₂Si₃O₁₀ and LiAlSi₂O₆ solid solution when its content is more than 35%.The CTE of the composites increased with the increase ofβ-Al₂O₃.The CTE of 68 wt%LABS glass-32 wt%β-Al₂O₃ is 3.15ppm/°C（300°C）,which matches that of silicon well.The conductivities of composites are determined by Li₂Al₂Si₃O₁₀.The activation energies calculated by Arrhenius equation of alkali ions of different composites ranges from 0.87 eV-0.90 eV.The variations of conductivities and activation energies indicate the composites have the alkali effect.2.The study of Li-Na-Al-B-Si-O（LNABS）glass-ceramicsThe sintering temperature of LNABS glass-ceramics is lower than 650^oC,which belongs to ULTCC（ultra-low temperature co-fired ceramics,ULTCC）,and the main phase is LiAlSi₂O₆.The thermal expansion coefficient of LNABS glass increases with the increase of Na₂O.When Na₂O content is 0.5%,the coefficient of thermal expansion（CTE）of LNABS glass-ceramics is 3.27 ppm/°C（300°C）,leading to an excellent theraml compatibility with silicon.Compared to the reported anodic bonding material,LNABS glass-ceramics have a better theraml compatibility with silicon over a wide temperature range from 60°C to 300°C.The study of broadband dielectric spectrum indicates the high temperature and voltage both increase its ionic conductivities.The ionic conductivities of LNABS glass-ceramics are more than 1?10^-8 S/cm when temperature is above 120°C and the glass phase conducts the long-range ionic hoping at high temperature.The study of broadband dielectric spectrum indicates,at the same temperature,ionic activation energy decrease as the bias increases.3.The study of the anodic bonding mechanism of Si-ULTCCThe LNABS glass-ceramics are successfully anodic bonded to Si substrate at a low temperautre（150°C）and voltage（200 V）.The studies of anodic bonding current,cross section and alkali ions concentration indicate that the low bonding temperature and voltage of Si-ULTCC anodic bonding are caused by the low activation energy of alkali ions.The studies on the alkali ions concentration areas of ULTCC（ultra-low temperature co-fired ceramics,ULTCC）by EDS and SIMS shows that the alkali ions are mainly concentrated in the glass phase,indicating that they mainly migrate through the glass phase.The Si-ULTCC anodic bonding mechanism are as follows:the alkali ions migrate toward cathode under high temperature and electric field,leaving non-bridge oxygen（NBO）at the bonding interfaces,which also forms a high space-charge electric field.The NBO drifts towards silicon and oxidized silicon under high space-charge electric field,which realized the anodic bonding of Si-ULTCC.4.The application of ULTCC substrate in MEMS pressure sensor and silicon-based micro-reactorA MEMS pressure sensor was encapsulated with ULTCC substrate.The pressure test shows this sensor exhibits high accuracy and good stability in a wide temperature range.A micro-reactor was designed and fabricated for 2-dimensional SnSe growth according to the confined space reaction mechanism.The SnSe nano sheets are deposited on Si substrate with a lateral size of 30 nm-110 nm and a thickness of 10 nm–70 nm.