High-K Metal Gate

In 2007, IBM developed an improvement to the transistor, the tiny on/off switch that serves as the basic building block of microchips. The company found a way to construct a critical part of the transistor with a new material, clearing a path toward chip circuitry that is smaller, faster and more power-efficient than previously thought possible. As important, the technology could be incorporated into existing chip manufacturing lines with minimal changes to tooling and processes, making it economically viable. IBM applied the technology to products with chip circuits as small as 45 nanometers starting in 2008. The technology, called high-k metal gate, substituted a new material into a critical portion of the transistor that controls its primary on/off switching function.

High-k Metal Gate (HKMG) technology is an advanced semiconductor fabrication technique that has proven critical in continuing Moore's Law, which states that the number of transistors in an integrated circuit doubles about every two years. As transistor dimensions have shrunk into the nanometer range, the traditional silicon dioxide gate dielectric used in CMOS transistors has run into several challenges, including increased leakage current. This is where High-k Metal Gate technology comes in.

The "high-k" part refers to the use of a material with a high dielectric constant (k) as the gate oxide, which is the insulating layer between the gate and the channel in a transistor. The "metal gate" part refers to the use of a metal gate electrode instead of a polysilicon one, which was used in traditional CMOS processes.

Key Benefits of High-k Metal Gate Technology

1. Reduced Gate Leakage: As mentioned above, the main benefit of using a high-k dielectric material is that it significantly reduces gate leakage current, which has become a major issue as transistors have become smaller. Despite being thicker than silicon dioxide, a high-k dielectric allows for a smaller equivalent oxide thickness (EOT), reducing leakage while maintaining good gate control over the channel.
2. Improved Performance: The use of a metal gate eliminates the 'depleted' polysilicon effect that can hamper the transistor's performance, resulting in faster transistor switching times and therefore faster overall chip performance.
3. Continued Scaling: As we continue to push the boundaries of miniaturization in electronics, traditional materials like silicon dioxide and polysilicon face physical and performance limitations. HKMG technology allows for the continued scaling of transistor dimensions without significant performance degradation or prohibitive leakage current levels.
4. Lower Power Consumption: Thanks to the significant reduction in leakage current, chips that use HKMG technology consume less power when idle. This makes them more energy-efficient, which is particularly beneficial for battery-powered devices like smartphones and laptops.
5. Better Threshold Voltage Control: The use of a metal gate allows for more precise control over the transistor's threshold voltage, which is critical for ensuring the transistor's proper operation.

Despite its benefits, the transition to HKMG technology was a significant challenge for the semiconductor industry, as it required substantial changes in the fabrication process. However, it has now become a standard part of the most advanced semiconductor manufacturing processes, helping to enable the latest and greatest electronic devices.