High Temp ASICs

Tekmos shipped our first 250C ASIC in July. It was made using the X-FAB 1.0u SOI process. I would like to discuss some of the things we learned from our first ASIC.

To begin with, while the first ASIC was designed to work at 3.3 volts, the process is better suited for 5 volt operation. The nominal transistor thresholds are high, and that causes severe performance degradation at 3.3 volts. We were able to make the design work, but there are enough issues with working at 250C without adding voltage problems.

We used a gate array technology to implement the design. Gate array technologies are based on a routing grid; the smaller the grid, the higher the gate density, and the lower the cost. Sometimes, you can make a tradeoff between a tighter grid, and the possibility that DRC errors will be introduced by the router. Fixing a handful of DRC errors is no big deal, so an extra hour of development time is a good tradeoff against perhaps a 5% reduction in cost. But in our initial pass with the SOI technology, we made a tradeoff that resulted in thousands of errors, and took about a week to correct. We plan to relax our grid on our next chip.

The design of the SOI transistor makes it impossible to route over it using metal 1. This is because of the substrate contacts we have to include in the source of each transistor. We compensated for that by including poly tunnels in our basic transistor design, and by providing additional room for the metal 1 routing in cells. This made our basic gate array "block" larger, and we did not increase the transistor sizes accordingly. As a result, the ratio of routing capacitance to gate capacitance rose, and we were forced to do a lot more post-route load fixing, that hurts performance, which was doubly painful considering the reduced performance with the lower operating voltage. With our larger grid, we will also make wider transistors.

We still have some characterization to do on the results, and I'll talk about that later.

Contact Bob Abrams, VP of Sales & Business Development for new product & data info at Contact Tekmos Sales

Date

2012-10-04