In 2000, I started a new company, Transparent Networks, focused on a large port count (1024x1024) photonic switch.
The optical switching was based on 3D MEMS mirrors, electrostatically tilting +/-10deg in two axes with about 0.001deg resolution. Each mirror had two electrodes per axis, thus four analog control channels with 15-bit resolution were needed for each mirror. To support 1024 channels with headroom for a yield loss, we designed a single 30x40 mm chip mirror array with 1200 mirrors, 30 rows by 40 columns, with each mirror in 1x1 mm cell, which required a dedicated logic.
Electrostatic drive required 120V. To support a quick response of all mirrors in 7 ms, we decided to implement a 10 kHz TDM refresh rate, with the update for each mirror in approximately 83 ns. To prevent the creep of mirrors in excess of 0.001deg from self-heating, we restricted the power to 2W for the entire chip electronics. We thus needed 4800 of super low power high voltage amplifiers on the chip.
So I was facing the state-of-the-art VLSI development as a supporting technology for the leading edge risky MEMS development.
I started a search for this custom ASIC vendor. One of my friends, a former VP of a prominent semiconductor company, recommended I work with Decicon, as they have been known for complex mixed signal IC designs working on the first silicon, and this was exactly what I wanted to reduce the development risk.
We started the program in December 2000. Decicon came up with a novel creative approach of driving mirrors with a very low power. They also managed to find a way of using 120V transistors with low Vgs, only ones we had available at this time with high density (1.2 um) CMOS.
Because of the chip complexity, we thought of doing initially only a small number of mirrors in the array to debug the design without stitching over the large chip and with a use of single reticle to control the cost. Decicon showed its creativity in this area, managing to do the layout without the stitching and with a single reticle, yielding about 80% (900) functional mirrors.
In August 2001, the first silicon came out from the fab. After few more weeks of integrating with mirrors and testing, I got the result: first silicon worked!
This 30x40 mm chip with millions of transistors and 4800 15-bit DAC, 4800 120V amplifiers, fast serial interface and all the row and column logic represents probably the largest mixed signal chip in the world. And making it working in the first pass is an outstanding accomplishment.
Thank you Decicon team. I can strongly recommend your services to anyone in need...
Dr. Janusz Bryzek
President and CEO,Transparent Networks
Managing Partner, BN Ventures
