Choosing the Right Technology Node for Your ASIC

There are many technology nodes available today, ranging from the most advanced 16 nm up through 1 u. So which one should you use for your ASIC? The answer depends on a combination of circuit size, speed requirements, and production volumes.

The biggest downside for the advanced technology nodes is the cost of the masks necessary to fabricate the wafers. The mask cost tends to double for each successive technology node, and is in the millions of dollars for the most advanced nodes. The manufacturing cycle is also longer for the more advanced nodes.

The advanced nodes offer greater circuit density, with the density roughly doubling for each node. This reduces the manufacturing costs, but are the savings worth the extra NRE charges?

And there is the issue of circuit speed. A DDR4 interface needs at least 65 nm for implementation. A PCIe G3 needs 28 nm. And a mixed signal part can be successfully implemented at 180nm or less. The application sets a lower limit on the technology node.

So how do you determine the optimum node? First, let the speed set the lower limit. And trade off the manufacturing cost versus the NRE cost for your anticipated volume. As a rough rule of thumb, the manufacturing savings should pay for the increase in NRE charges within 6 months.

Tekmos has pioneered the use of stacked die in an ASIC. Our idea is that you can purchase much of the IP such as processors and RF modules in die form, and use the ASIC for the rest of the system and to interconnect the other die. A huge advantage of this approach is that you can reduce the technology requirements for the ASIC since the purchased IP contains the functions that require the advanced technology nodes. We worked an application that required a DSP function, high speed ADC and DACs, and a processor with large amounts of Flash and RAM. A single chip implementation would require a 28 nm process and the licensing of multiple IP blocks. Instead, we could offer a 180 nm solution with a million-dollar reduction in the NRE.

ASICs have a deserved reputation for being expensive. But they don't have to be. Analyzing your application and making intelligent decisions can reduce your costs and produce a superior product.