Intel’s Hot New Tri-Gate Processors

By Barry Pangrle
Intel announced its newest third-generation Core processors on April 23rd. There has been much anticipation surrounding these new chips from Intel, largely because of their new 22nm tri-gate process technology used to fabricate these devices.

Figure 1, from the presentation entitled, “Intel’s Revolutionary 22nm Transistor Technology,” by Mark Bohr and Kaizad Mistry, shows the dramatic improvement in performance at lower voltages for the new tri-gate technology.

Fig. 1. Delay vs. Voltage for 22 nm Tri-Gate and 32 nm Planar.

Intel is calling its new third-generation processors a “tick-plus” in its tick tock model. Typically, a “tick” represents the move of a previous architecture to a new process technology and then the “tock” is a new architecture on that same newer technology node. In this case, the CPU architecture for the new “Ivy Bridge” parts is mostly the same as for the older “Sandy Bridge” parts, but the graphics portion of the newer chips has received notable enhancements over the previous version; hence the tick-plus designation.

The various markets for processors have been carved up roughly based on the Thermal Design Power (TDP) of the processors. Table 1 below shows a typical breakdown for the different applications and the TDP ranges for those parts. Manufacturers often will try to squeeze the most performance out of their designs within the power envelope for the target market segment.

We’re going to take a look at the top-end high-performance desktop parts, which Intel calls Core i7, to compare the old 32nm Sandy Bridge parts to the new 22nm tri-gate Ivy Bridge parts. Table 2 shows two 32nm parts and three new 22nm parts. A more extensive comparison table is available here. One thing that immediately stands out is that the CPU clock speeds for the fastest 32nm and 22nm parts are the same and that the GPU clock is actually slower in the newer 22nm parts. The architectural improvements of the new HD Graphics 4000 vs. HD Graphics 3000, and the boost in memory bandwidth from 21 GB/s to 25.6 GB/s, enable the new parts to outperform the older parts in graphics and slightly from a CPU standpoint. Still, I find it somewhat surprising that the clock speeds weren’t increased.

So, other than scaling, what has the new technology brought? Well the new top end part (i7 3770K), with about 20% more transistors, is now rated at a TDP that is about 19% lower. So in this case, the new technology has really primarily been used to provide more energy efficient parts and it’s clearly a nod to power as the primary driver.

Another interesting note from Table 2 is that while the TDP has been reduced by about 19%, the area has been reduced by closer to 26%, which means that the power density, or the amount of power that needs to be dissipated per square millimeter, has actually gone up. This could bring up some interesting cooling issues.

Figure 2 below actually is from Intel’s Desktop 3rd Generation Intel Core Processor Family and LGA1155 Socket Thermal Mechanical Specifications and Design Guidelines (TMSD) (Figure 2.1) available here.

Fig. 2. Processor Package Assembly Sketch. (Source: Intel)

A number of online sites (notably here and here) have mentioned that Ivy Bridge seems to heat up rather quickly as the voltage is increased. This is probably of little concern to most customers, but for those who buy high-end parts for overclocking, this has raised some eyebrows. It appears that at least a partial answer to this issue may have been found here. As diagramed in Figure 2, IHS stands for Integrated Heat Spreader and TIM for Thermal Interface Material. Looking at packaged parts that had the IHS pried apart from the die and the substrate, revealed that rather than using a fluxless solder approach, as used in Sandy Bridge, a TIM paste with presumably a much lower (order of magnitude) thermal conductivity has been used, which would severely impact the ability to cool these parts. It will be interesting to see if Intel stays with the TIM paste or goes back to fluxless solder. In the meantime, it appears that the serious overclockers will have to play a waiting game or perhaps try even more extreme measures to push these new parts to ever-higher limits.

—Barry Pangrle is a solutions architect for low power design and verification at Mentor Graphics.