Printing low power-low performance microprocessors onto organic materials will open a wide range of cost effective alternatives to silicon-based embedded devices, but resolution remains a problem.
By John Blyler, Contributing Senior Editor, Semiconductor Digest (Former Editor-in-Chief, Chip Design Magazine
The year was 1971. Intel had just introduced the first commercially available 4-bit microprocessor. Since that time, silicon-based semiconductors have ruled the world of electronics. Moore’s Law has successfully predicted the relentless march to ever high performing and high power microprocessors.
At roughly the same time, work began on semiconductors of a different type – organic. Since organic semiconductors rely on molecules, there would be intrinsically worse performers than silicon due to mobility of the carriers. However, what organic semiconductors lacked in clock speed would be compensated for in power consumption, material application advantages and – eventually – low cost manufacturability. This last benefit is important.
“The advantage of using organic semiconductors is that they can be applied over large surfaces by techniques of printing,” explained Jan Genoe, a researcher at IMEC. “Silicon needs to be mono-crystalline, which implies that you must start with very pure material – typically not very flexible or bendable.”
By contrast, organic semiconductors can be deposited on any printable surface, such as a card board box. Genoe cites the example of a small microprocessor-based circuited printed onto a cookie box. Each time a cookie is taken from the box, the electronics could calculate how many calories have been consumed. A less appetizing but perhaps more useful application would be in medicine packages, where the electronics would trace when or if patients actually take their medicine.
In the past, such functional has been demonstrated with organic circuits that perform basic analog-to-digital conversion (ADC) that provide a sensor readout, perhaps to an organic RFID tag. But now that same functionality can be performance with a low-power, low-performance microprocessor, which opens the door to more complex applications.
Recently Imec, Holst Centre and the Katholieke Universiteit Leuven report the world-first functional 8-bit microprocessor made by organic thin-film transistors processed directly (i.e. without transfer) onto flexible plastic foil. Featuring over 4,000 transistors, these microprocessors contain complex control logic and variable data paths. The microprocessor foil operates on supply voltages (VDD) between 10 and 20V at a clock frequency up to 6Hz. The power consumption of the microprocessor is typically 92µW at 10V supply voltage – ideal for low performance applications.
But challenges remain. Genoe explains that, in principle, the processes are portable to commercial printing applications. That has yet to happen. The problem is one of resolution. Today’s printing technology allows print on one-tenth of a millimeter material. But 8-bit organic microprocessors need to be accurate up to 5 micron or one two-hundredths of a millimeter, notes Genoe. This means that current printing tools need to improve by a factor of 20 times.
While this goal is not impossible, it will be challenging for printers due to the bulk size and high-vibrational environment of most printing machines.
What is the roadmap for these organic computers? Genoe says that the next step, after proving the technology was feasible, is to collaborate with people in the printing industry. In terms of applications, another area being explored is the distribution of these very slow but extremely low power organic processors that communicate to one high performance silicon processor. Such a heterogeneous processor network might include remote sensor and data-processing applications that feedback to a central server-grade computer.
Recent trends in embedded systems have shown the need for very low power, low performance processors. The capability of manufacturing such devices on ordinary materials opens up a world of additional possibilities.
From the Chip Design Magazine / Low Power Engineering archive, first published in Oct 2011. — JB
