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What does moving to a new manufacturing process actually accomplish? Intel’s move to 45nm isn’t a simple die shrink. Instead, the company is implementing new technologies to enable greater efficiency. The key new technology implanted is Intel’s high-k plus metal gate process.
Intel’s transistor-design innovation recognizes that silicon dioxide had to go, since this dielectric material wasn’t doing a good enough job of stopping leakage current from flowing through the gate oxide. For its new 45nm process, Intel switched to a material that has a higher dielectric constant (K value). The high K material chosen for the new gate insulator? The element Hafnium now replaces silicon dioxide, but alas, the previous metal gate interconnects don’t like Hafnium and have been replaced by a new metal material that Intel hasn’t disclosed.
Atomic number 72 on the periodic table, Hafnium has a number of uses, the most exotic of which is its ability to absorb neutrons, so it’s used in control rods in nuclear reactors. So Intel’s new transistors sport both new dielectric material and a mystery metal gate electrode. Hafnium is itself a metal and will be featured in future transistors from IBM. Intel must believe there is a competitive advantage to being coy about what they chose for the gate electrode material.
Intel’s 45nm process, with its new transistor technology, yields a number of key advantages:
- About twice the transistor density
- A 30% reduction in transistor switching power
- Either a 20% improvement in transistor switching speed or a 5X reduction in source-drain leakage power
- A better than 10X reduction in transistor gate oxide leakage
All this affects one the key issues of high-performance transistors: current leakage. Less leakage results in more efficient power usage at the same clock speed as previous generations. By the same token, increasing transistor switching speeds allows for higher clock rates.
Source-drain leakage is dependent on the transistor threshold voltage. The use of Hafnium allows them to have a thicker gate insulator which Intel suggests allows a 5X reduction in gate leakage (current flowing through the gate into the substrate). Note that gate leakage is exponentially related to the thickness of the insulator.
The claimed 10X reduction in source-drain leakage shouldn’t have anything to do with the gate insulator. It’s a little confusing, but the source-drain leakage is part of the same transistor design that allows them to run 20% more current (getting higher switching speeds). The key is that CPUs based on the new 45nm process can run at the higher clock rate or can keep the voltages down and match the speed of the 65nm. The lower voltages are probably what would then allow a 10x reduction in source-drain leakage.
Note that the lower power at a given clock frequency comes from having smaller transistors. That 30% reduction in switching power comes from the smaller transistor size. Low leakage is all about saving power at idle and in various power management C-states. (For more on leakage issues and power management, check out Scott Gardner’s article on power management technology.)
Now that we have some understanding of what’s going on under the hood of Intel’s 45nm process, let’s take a look at the new Core 2 architecture. Continued…