Everybody pretty much knows the score on BiCMOS. The bipolar transistors are very handy for analog designers, but when you get right down to it, the process, with 20-some masks for a design with minimal interconnect, is just too expensive to justify. And everybody pretty much knows the score on small companies owning fabs—it's a financial dead end. Or at least so one might believe until they had investigated the German mixed-signal ASIC house—and soon to be foundry—PREMA.

PREMA, if you haven't met them, is an exception to both rules. The company has mixed-signal 0.6-micron and 0.25-micron Silicon BiCMOS processes that require only 11 masks for a 2-metal design. The 11 masks is the base process, which offers a 20V npn and a 25V pnp, the option of smaller 10V DMOS devices, and logic density of up to about 70k transistors per square mm. Two more masks will get you 80V bipolar devices. Obvious applications include intelligent driver devices, sensor signal processors, and control circuitry in high-voltage loops.

The reason PREMA can offer BiCMOS in 11 masks, according to CFO Rudolf Enders, traces back to the beginnings of the company in 1970. The Mainz, Germany firm was founded by two physicists as a precision-measurements vendor. At some point in the company's growth, an instrument design required a mixed-signal IC that wasn't readily available. So like good physicists anywhere (at Tektronix, for instance) they built a fab.

Now the story gets interesting. Again in the spirit of physics, the PREMA people couldn't leave well enough alone. So they started experimenting with the process, and concluded that an ion implant machine capable of imparting really high energies to the ions to make really deep implants could save many mask layers on BiCMOS. So not stopping at owning a fab, they invented and built their own high-energy implanter. They turned out to be correct, and that is the explanation for the 11-mask BiCMOS process.

Other advantages come up as well. Joachim Scheerer, managing director at PREMA, explains that photodiodes generally have a problem with dark-current. The reason, he says, is that the diode structure depends on a rear diffusion that ends up doing considerable damage to the silicon lattice. The dislocations increase the residual current. But PREMA's high-energy impanter can create the doped region through the top of the wafer, minmizing lattice damage. The result is photodiodes with dramatically lower dark current, Scheerer says. This raises a number of possibilities, including motion or position encoders that can work in optically difficult environments, or photometric applications.

One of the constant struggles with BiCMOS is keeping the digital noise out of the precision analog circuitry for which, presumably, the designers chose the process in the first place. At least for lower-speed, low-density logic, PREMA has an interesting answer here as well: a version of bipolar current-steering logic they call constant-current logic, or CCL. As the name implies, the logic gates switch a constant current between outputs, rather than turning current on and off, eliminating much of the switching noise of conventional digital circuits. Real veterans will be reminded of i-squaredL.

With a proprietary process and a proprietary logic family, PREMA raises the question of the design interface. Heretofore the company has provided its own models and characterization with some outside assistance, as well as its own P-cell libraries, logic libraries and memory compiler for the digital circuitry. This gives users enough libraries for skilled analog designers to do cell-based design, and for conventional synthesis tools to work on the digital side. But Scheerer says that the company is looking to bring more brand-name library vendors into the picture as well, particularly for memory compilers.

Put it together, and you get an interesting package. BiCMOS with high-voltage capabilities, high-performance photodiodes, a real ASIC design interface, and the rapid turn-around and low NRE that come with the small number of masks. It's enough to upset conventional thinking, at least for the range of applications that PREMA serves.