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Why are inductors not used in integrated circuits ?

Inductors are not commonly used in integrated circuits (ICs) due to several practical challenges and limitations associated with their implementation at the miniature scales of modern semiconductor technology. The primary reasons include size, parasitic effects, fabrication complexity, and the desire for cost-effective and compact IC designs. Here’s a detailed explanation:

  1. Size Constraints:
    • The physical size of inductors is a significant constraint in the integration of inductors into ICs. Inductors typically require a substantial amount of space, and as the dimensions of IC components continue to shrink in semiconductor technology, integrating bulky inductors becomes increasingly impractical. The space efficiency is crucial in IC design to accommodate a large number of components on a small chip.
  2. Parasitic Effects:
    • Inductors in ICs are prone to parasitic effects, such as mutual inductance between adjacent inductors and coupling with other components on the chip. These effects can result in crosstalk, interference, and performance degradation of the overall IC. Managing and mitigating parasitic effects in integrated inductors add complexity to the design and compromise the performance of neighboring components.
  3. Fabrication Complexity:
    • Fabricating inductors using semiconductor processes is challenging and involves additional processing steps beyond those used for typical IC components like transistors and resistors. Unlike resistors and capacitors, which can be easily integrated into standard CMOS (Complementary Metal-Oxide-Semiconductor) processes, creating inductors often requires specialized fabrication techniques. These additional steps increase the cost and complexity of IC production.
  4. Limited Frequency Range:
    • Inductors are typically used in applications requiring high-frequency signals. In ICs, the operating frequencies are generally within the radio frequency (RF) and microwave range. However, the inherent capacitance and parasitic effects of semiconductor materials limit the effectiveness of inductors at these frequencies. Other passive components, such as capacitors, are more suitable for high-frequency applications in ICs.
  5. Power Dissipation:
    • Inductors have resistive losses that lead to power dissipation in the form of heat. In an IC, managing heat dissipation is crucial to avoid thermal issues that can affect the reliability and performance of the entire circuit. The resistive losses in inductors may contribute to increased power consumption and thermal challenges in miniaturized IC designs.
  6. Alternative Technologies:
    • IC designers often prefer alternative technologies to achieve energy storage and filtering functions traditionally associated with inductors. Capacitors, for instance, are widely used in ICs due to their smaller size, ease of integration, and lower sensitivity to parasitic effects compared to inductors. On-chip inductors are sometimes replaced by LC (inductor-capacitor) resonators, which are more compatible with IC fabrication processes.
  7. Economic Considerations:
    • Cost-effectiveness is a critical consideration in IC design. The additional processing steps, larger chip area requirements, and potential yield losses associated with integrating inductors can make ICs with inductors economically less viable compared to alternatives that achieve similar functionalities with capacitors, resistors, and other components.

In summary, while inductors are fundamental components in many electronic systems, their integration into modern integrated circuits faces substantial challenges related to size, parasitic effects, fabrication complexity, frequency limitations, power dissipation, and economic considerations. These challenges have led to the widespread use of alternative components and technologies that better suit the constraints and requirements of semiconductor processes, allowing for the development of compact, high-performance, and cost-effective ICs.

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