Fig. 1. Applications of SiC-based composite substrates

Fig. 2. Schematic diagrams of wafer bonding process^[109]. (a) PAB; (b) room-temperature SAB

Fig. 3. Smart Cut process flowchart diagram^[118]

Fig. 4. Characterizations of SiC/Si bonding results and schematic diagrams of SAB bonding process. (a)(b) Optical images after annealing at 150 ℃ and 300 ℃, respectively^[34]; (c)(d) TEM images of the interface after annealing at 150 ℃^[34]; (e)(f) TEM images of the interface after annealing at 300 ℃^[34]; (g) SAB process diagram^[31]; (h)(i) HRSTEM and EDS results of the interface before and after annealing at 750 ℃^[31]

Fig. 5. Schematic diagrams of Ga₂O₃/SiC bonding process and characterizations of bonding results. (a)(b) BF STEM images before and after annealing at 473 K^[45]; (c)(d) HAADF STEM images before and after annealing at 473 K^[45]; (e)(f)(g) differential SSTR process measurements: thermal conductivity of the 4H-SiC substrate, thermal conductivity of the Ga₂O₃ layer, and effective TBR at the Ga₂O₃/4H-SiC interface^[138]; (h) schematic diagram of high temperature hydrophilic bonding of β-Ga₂O₃ and 4H-SiC wafers ^[59]

Fig. 6. Analysis of recrystallization at the bonding interface^[44]. (a) HRTEM image of the interface of InP/SiO₂ at room temperature; (b) FFT-DP analysis of amorphous SiO₂; (c) HRTEM image of amorphous SiO₂(inset: EDS image of the bonding interface); (d) HRTEM image of the 300 ℃ annealed interface; (e) FFT-DP of In₂O₃ with a zone axis of [011]; (f) crystal structure of In₂O₃; (g) 600 ℃ annealed interface; (h) FFT-DP of InPO₄ with a zone axis of [110]; (i) crystal structure of InPO₄

Fig. 7. Experimental process diagrams of 4H-SiC bonding by PAB method and characterizations of bonding results^[38]. (a) 4H-SiC wafers etched by oxygen plasma and immersed in methanol solution; (b) pre-bonding of two SiC wafers; (c) strong bonding of pre-bonded samples under high temperature and high pressure; (d) TEM images of the cross section of the bonded sample; (e) EDX line scan image of bonding interface

Fig. 8. Characterizations of 4H-SiC bonding results by SAB method^[53]. (a)(b) TEM images of standard SAB bonding interface before and after annealing; (c)(d) TEM images of the Si-containing ion beam modified SAB bonding interface before and after annealing; (e)(f) EDS line scan images of standard SAB bonding interface before and after annealing; (g)(h) EDS line scan images of Si-containing ion beam modified SAB bonding interface before and after annealing

Fig. 9. Sensor configuration, working principle and test results^[144]. (a) Schematic diagram of the SiC fiber-optic pressure sensor; (b) F-P cavity interference in the sensor and the interference spectrum; (c) curves of the F-P cavity length response to external pressure during three loading pressure experiments; (d) sensor pressure response curves for loading and unloading pressure conditions over three cycles; (e) sensor pressure response curves at 23‒400 ℃ and under 0‒800 kPa; (f) F-P cavity length as a function of temperature under 0 kPa

Fig. 10. Setting and statistical study of Q factor in microresonators^[148]. (a) Schematic diagram of measuring device used to characterize the nonlinear optical process in SiC microresonator (AFG: arbitrary function generator, CTL: continuous wave tunable laser, PC: polarization controller, EDFA: erbium-doped fiber amplifier, UV-VIS: ultraviolet-visible spectrometer, OSA: spectrometer, PD: photodetector); (b) TE mode resonances and their fitting (calculated intrinsic Q value is 7.1×10⁶); (c) intrinsic Q-factor histograms of TE mode; (d) TM mode resonances and their fitting (calculated intrinsic Q value is 7×10⁶); (e) intrinsic Q-factor histograms of TM mode. The insets in (c) and (e) show the electric field distribution in the numerical simulation of the basic TE and TM modes, and the arrow indicates the electric field vector

Fig. 11. Test results^[39]. (a) TBR of SiC/SiC bonding interface and (b) SiC thermal conductivity of 1 μm 4H-SiC film at various temperatures from 300 K to 750 K; (c) benchmark of thermal properties reported for SiC heterogeneous integration with different materials based on wafer bonding or epitaxy (1 μm 4H-SiC/4H-SiC substrate is a baseline structure specifically for monitoring the material quality and for thermal characterizations)