Etched field-oxide isolation:
Etched field-oxide isolation is a technique used to create isolated active areas in integrated circuits. In this technique, a layer of field oxide is created on the silicon substrate, and then the active areas are defined by selectively etching away the field oxide.

Local Oxidation of Silicon:
Local Oxidation of Silicon (LOCOS) is another technique used to create isolated active areas in integrated circuits. In this technique, a thin layer of silicon nitride is deposited on the silicon substrate, and then a layer of silicon dioxide is grown over it. The silicon nitride acts as a mask, preventing the growth of silicon dioxide in certain areas. The areas where the silicon dioxide grows are the isolated active areas.

Combination of both techniques:
In some cases, both etched field-oxide isolation and local oxidation of silicon techniques are used together to create isolated active areas in integrated circuits. This combination of techniques allows for more precise control over the location and size of the isolated active areas.

Advantages of isolated active areas:
- Reduced parasitic capacitance: Isolated active areas help in reducing the parasitic capacitance between different components in the integrated circuit. This leads to improved circuit performance and lower power consumption.
- Improved device isolation: Isolation of active areas prevents unwanted electrical interactions between neighboring devices. This enhances the overall reliability and performance of the integrated circuit.
- Enhanced device integration: Isolated active areas allow for better integration of different components on the same chip. This enables the design and fabrication of more complex and sophisticated integrated circuits.
- Better noise immunity: Isolated active areas help in reducing the impact of noise and interference on the performance of the integrated circuit. This results in improved signal integrity and overall circuit reliability.

Conclusion:
The combination of etched field-oxide isolation and local oxidation of silicon techniques is commonly used to create isolated active areas in integrated circuits. These isolated active areas provide various advantages such as reduced parasitic capacitance, improved device isolation, enhanced device integration, and better noise immunity.