# Development Status of Key Technologies for Optoelectronic Integrated Circuit Manufacturing
## 3 Manufacturing of Optoelectronic Integrated Circuits
### Integration Method
#### 3.2.2 Hybrid Integration  
Hybrid integration is the most widely studied optoelectronic integration technology in which optoelectronic components are integrated with various functions on the substrate material through direct placement or a bonding process [47; 48; 49; 50]. Among them, the direct placement involves using flip-chip bonding or mounting process, placing the pre-fabricated III-V material laser on the surface of the Si photonic chip, and completing the electrical connection through solder balls to realize the hybrid integration of the light source and the Si optical waveguide device [51]. [PERSON] et al. designed a silicon photonic transmitter chip without temperature control by integrating a III-V material semiconductor optical amplifier (SOA) on an SOI material substrate using flip-chip technology [52]. Flip-chip welding technology renders the design of Si optical components and SOA flexible and improves SOA thermal conductivity. End-face coupling requires flip-chip welding with a high degree of accuracy. The flip-chip welding technology is mature and can also be used effectively because of the optical gain characteristics of III-V materials. However, the high alignment accuracy requirements result in higher process costs. Bonding involves integrating the III-V material epitaxial layer with Si optical components. Because of the high alignment tolerance of the bonding process, compared with the direct placement process, this method exhibits a superior alignment accuracy advantage [29]. The bonding process is categorized into direct bonding and adhesive bonding. Direct bonding involves directly contacting two smooth, flat, and clean wafers without using bonding materials. [PERSON] and [PERSON] et al. [53; 54] proposed forming a bond between the two wafers under the action of the interface bond. Adhesive bonding integrates inter-wafer bonding using specific bonding materials. Benzocyclic (BCB) as a binder is mature, and BCB exhibits a strong bonding effect with excellent flatness and thermal stability. Compared with direct bonding, the thermal conductivity of the BCB material is poor, which results in poor heat dissipation of the integrated device and reduces light source performances. The \"cold bonding\" process proposed by [PERSON] et al. [55] is similar to the developed mainstream \"low temperature bonding\" principle and can effectively address the aforementioned problems. The room-temperature bonding process should be used for future bonding technology development [56]. [PERSON] et al. [57] developed a high-speed integrated tunable optical delay line using a novel preparation method. The substrate material of this delay line is silicon material, and the waveguide material is silicon nitride optical waveguide and lithium niobate optical waveguide. The lithium oxide material is a thin-film material, and the adopted BCB-based bonding process renders the process flexible and does not require a chemical mechanical polishing process. In 2019, [PERSON] et al. [58] used a hybrid integration scheme in which the chip and circuit were bonded by a gold wire to prepare a high-gain four-channel miniaturized optical receiver module device, which reduces the size and power consumption of the communication system and has numerous application areas.