I. Hybrid Integrated Circuits and Technologies
The development trends of hybrid integration technology are: ① Using multilayer wiring and carrier bonding technology to assemble and interconnect monolithic semiconductor integrated circuits, achieving secondary integration and fabricating complex, multifunctional, high-density, large-scale hybrid integrated circuits. ② Passive networks are developing towards greater density, precision, and stability, and sensitive elements are integrated into their passive networks to create integrated sensors. ③ Developing high-power, high-voltage, and high-temperature resistant hybrid integrated circuits. ④ Improving film deposition technology to make the manufacturing process of thin-film active devices practical. ⑤ Assembling miniature chip-shaped leadless components and devices using substrates with interconnects to reduce the price of electronic devices and improve their performance.
There are two common film deposition techniques used in manufacturing hybrid integrated circuits: screen printing and vacuum deposition. Films manufactured using the former are called thick films, with a thickness generally greater than 15 micrometers. Films manufactured using the latter are called thin films, with thicknesses ranging from hundreds to thousands of angstroms. If the passive network of a hybrid integrated circuit is a thick-film network, it is called a thick-film hybrid integrated circuit; if it is a thin-film network, it is called a thin-film hybrid integrated circuit. To meet the requirements of miniaturization and integration of microwave circuits, microwave hybrid integrated circuits also exist. These circuits are further divided into lumped-parameter and distributed-parameter microwave hybrid integrated circuits based on the concentration and distribution of component parameters. Lumped-parameter circuits are structurally similar to general thick-film and thin-film hybrid integrated circuits, but require higher precision in component dimensions. Distributed-parameter circuits are different; their passive networks are not composed of externally distinguishable electronic components, but are entirely composed of microstrip lines. Due to the high precision requirements for microstrip line dimensions, distributed-parameter microwave hybrid integrated circuits are mainly manufactured using thin-film technology.
II. Hybrid Integrated Circuit Design and Methods
1. Design and Planning
The research and development of mixed-signal integrated circuits should begin with market demand, selecting a research and development objective, then determining the system definition and system specifications of the mixed-signal integrated circuit, and on this basis, developing and selecting appropriate algorithms.
2. System Modeling
Once the algorithm is determined, it is mapped to a specific structure to facilitate circuit design and overall verification of each module. At this point, the system functional behavior and non-functional constraints of the mixed-signal integrated circuit must be detailed. Furthermore, considering the mixed characteristics of the circuit, it must be specified in different ways, using continuous time-varying and discrete time-varying methods, which can be separated using a block diagram structure. Currently, designers commonly use software such as Matlab, C, SystemC, and SPW for system design. Matlab is widely used by algorithm engineers and, as the preferred development tool for DSP algorithms, has a large user base. SystemC is a language specifically developed for integrated circuit system design, while SPW is the most widely used system-level design tool, with numerous applications in communications, video, and other fields.
3. Digital/Analog Circuit Division
At this stage, it is necessary to distinguish between analog and digital circuits based on their functions. Digital circuits are used to process discrete signals, while analog circuits process continuous signals.
4. Circuit-level design and simulation
Circuits can be characterized by specific components, such as operational amplifiers, transistors, capacitors, and logic gates. Mixed-signal integrated circuits consist of both digital and analog parts. Analog circuits are generally designed entirely in a bottom-up manner, employing a full-custom layout design, verification, and simulation. Digital circuits, on the other hand, typically use a top-down design process, involving register-transfer level description, register-transfer level simulation, testing, synthesis, and gate-level simulation. Then, both types of circuits are placed on a mixed-signal verification platform for mixed-signal simulation.
This type of hybrid simulation can be a combination of register-transfer level digital circuits and transistor level analog circuits, or a combination of gate-level or transistor-level digital circuits and analog circuits. Currently, designers primarily use analog and mixed-signal tools and technologies provided by the three major EDA tool vendors: Mentor Graphics, Synopsys, and Cadence, for hybrid simulation.
5. Layout-level design and post-simulation
In these two phases, the integrated circuit-level design, combined with relevant physical implementation processes, involves layout design, design rule checking, layout verification, and parasitic parameter extraction for the relevant analog and digital circuits. Afterwards, post-simulation of the entire system's mixed-signal circuits is performed using a relevant mixed-signal verification platform.
6. Chip fabrication
After post-simulation is completed, the geometric data standard (GDSII) format file can be sent to the PCB manufacturer to make a mask. Once the mask is made, it can be sent to the production line for fabrication.
III. Types of Hybrid Integrated Circuits
There are two film deposition techniques used to manufacture hybrid integrated circuits: screen printing and vacuum deposition. Films produced using the former are called thick films, typically with a thickness of 15 micrometers or more, while films produced using the latter are called thin films, with a thickness between several hundred and several thousand angstroms. If the passive network of a hybrid integrated circuit is a thick-film network, it is called a thick-film hybrid integrated circuit. If it is a thin-film network, it is called a thin-film hybrid integrated circuit. To meet the requirements of miniaturization and integration of microwave circuits, microwave hybrid integrated circuits exist. Based on the concentration and distribution of component parameters, these circuits are divided into lumped-parameter and distributed-parameter microwave hybrid integrated circuits. The structure of lumped-parameter circuits is the same as that of conventional thick-film hybrid integrated circuits, the difference being that the component dimensions are more precise. Distributed-parameter circuits are different. Their passive networks are not composed of visually distinguishable electronic components, but are entirely composed of microstrip lines. Microstrip lines have high dimensional precision, therefore thin-film technology is mainly used to manufacture distributed-parameter microwave hybrid integrated circuits.
