Switching speed of ICs vs gate length

• ZeroFunGame
In summary, the smaller the gate length of a MOSFET, the higher the maximum operating frequency due to the relationship between gate capacitance and input current. However, as technology advances, second order effects start to dominate and limit the speed of ICs. This is because the input to output capacitance forms a low pass filter known as a Miller Integrator, which restricts the speed of amplifiers and logic gates.
ZeroFunGame
TL;DR Summary
Why is it that the smaller the gate length, the higher the max operating frequency becomes? In particular, I think I saw somewhere that a 6 um gate length, seems to limit ICs to 100kHz, where as 1 um is around 1MHz (all rough ball bark numbers, and can be persuaded otherwise). Was wondering if there are fundamental physical limits here that correlates the switching speed to gate length?
Why is it that the smaller the gate length, the higher the max operating frequency becomes? In particular, I think I saw somewhere that a 6 um gate length, seems to limit ICs to 100kHz, where as 1 um is around 1MHz (all rough ball bark numbers, and can be persuaded otherwise). Was wondering if there are fundamental physical limits here that correlates the switching speed to gate length?

Whenever I see words "frequency" and "size" together I start to think about capacitance.

Doesn't mean it is a problem at the frequencies you listed (can be, I just don't know), but it definitely starts to be a serious problem when you get to higher frequencies.

berkeman
ZeroFunGame said:
Summary: Why is it that the smaller the gate length, the higher the max operating frequency becomes? In particular, I think I saw somewhere that a 6 um gate length, seems to limit ICs to 100kHz, where as 1 um is around 1MHz (all rough ball bark numbers, and can be persuaded otherwise). Was wondering if there are fundamental physical limits here that correlates the switching speed to gate length?

Why is it that the smaller the gate length, the higher the max operating frequency becomes? In particular, I think I saw somewhere that a 6 um gate length, seems to limit ICs to 100kHz, where as 1 um is around 1MHz (all rough ball bark numbers, and can be persuaded otherwise). Was wondering if there are fundamental physical limits here that correlates the switching speed to gate length?

To first order, the answer is simple. The capacitance C of a MOSFET gate is proportional to Cox*W*L, where Cox is the gate oxide capacitance, W is the gate width, and L is the gate length. The current I of a MOSFET is proportional to μ*Cox*W/L, where μ is the carrier mobility. In an IC, you basically have a series of MOSFETs, where the output current of one MOSFET drives the input (the gate, with its capacitance C) of the next MOSFET. Now if you have a current I driving a capacitance C, I = C dV/dt. So dV/dt, which is how fast the circuit operates, is proportional to I/C, which equals μ/L^2. So as the gate length gets shorter, the circuit runs faster. For many years, this drove the IC industry, and ICs got smaller, faster, and cheaper as L scaled down. Today, these simple relationships no longer hold, because second order effects dominate. So things are not speeding up nearly as fast as they did in the past.

essenmein and ZeroFunGame

1. What is the relationship between the switching speed of ICs and the gate length?

The switching speed of ICs (integrated circuits) is directly affected by the gate length, which is the length of the transistor gate in the IC. As the gate length decreases, the switching speed of the IC increases.

2. How does the gate length impact the performance of ICs?

The gate length has a significant impact on the performance of ICs. A shorter gate length allows for faster switching speeds, which results in higher performance and efficiency of the IC.

3. Is there a limit to how small the gate length can be in ICs?

Yes, there is a limit to how small the gate length can be in ICs. As the gate length decreases, the effects of quantum tunneling and leakage currents become more prominent, which can negatively impact the performance of the IC. This limit is constantly being pushed by advancements in technology.

4. Are there any trade-offs between gate length and other factors in IC design?

Yes, there are trade-offs between gate length and other factors in IC design. While a shorter gate length allows for faster switching speeds, it also results in higher power consumption and increased heat generation. Therefore, designers must carefully balance these factors to optimize the performance of the IC.

5. How do advancements in technology impact the gate length of ICs?

Advancements in technology have allowed for the gate length of ICs to decrease significantly over the years. This has led to faster switching speeds and higher performance of ICs. However, as the gate length approaches its physical limit, new technologies and techniques must be developed to continue improving the performance of ICs.

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