Silicon sensing

Written by: Tom Shelley | Published:

A technology used to produce smaller, more powerful microchips is helping to make a whole new generation of compact, robust sensors. Jonathan Ward reports

The need to put ever-smaller transistors into chips has resulted in some ingenious technological leaps. One of those promises to give regular silicon chips the ability to sense and measure their environment.
The new technology is the brainchild of Irish startup ChipSensors, which has been developing its concept for just over a year and says it will have product on the market at the start of 2008.
At well as monitoring building and air conditioning systems, the tiny chips could replace data recording modules that are used to monitor foodstuffs.
At the heart of ChipSensors’ technology are the so-called ‘low-k dielectrics’ that are placed between the layers of transistors in a modern MOSFET chip to insulate them from each other. Conventionally, these insulating layers were made of silicon dioxide. As transistors became smaller and were packed closer together, the layers of silicon dioxide become ever thinner and began to cause problems. The search began for better insulators – and several porous materials are now used.
Seeing the wide uptake of porous insulating materials in chip manufacture was to provide a moment of insight for silicon chip designer – now ChipSensors CEO – Tim Cummins. Cummins had begun his career designing sensor integration circuitry for a major automation company. As a result, he knew that porous materials had provided the operating principles behind many types of sensor for decades. Now that the industry had developed techniques for the accurate application of these materials in the chip manufacturing process, perhaps it would be possible to integrate sensing elements directly into the chips as they were made.
According to Cummins: “By piggy-backing on mainstream semiconductor technology developments in this manner, we are opening the door to true low-cost and high volume scalability for wireless sensors."
Porous materials work well as sensors because, as the content of the pores changes, so do the electrical characteristics of the material. Changes in temperature, humidity or the chemical make-up of the atmosphere all have an effect. By carefully controlling the geometry of the pores, it is even possible to make sensors that react to pathogen particles.
By deliberately building tiny capacitors into chip designs using porous dielectric materials – together with the sensitive analogue to digital conversion circuitry necessary to measure these changes in properties – Cummins and his colleagues have produced a fully integrated sensor-on-a-chip. ChipSensors technology can be manufactured on existing chip production equipment and calibrated inside the silicon fabrication facility. As the chips are otherwise entirely conventional in design, memory and processing capability can also be built into the same integrated circuit.
The first products to use ChipSensors’ patented technology will provide various combinations of temperature, humidity and light sensing. Gas and pathogen detectors will follow as the technology evolves. Initial markets for the chips will include heating, lighting and ventilation control circuitry for buildings but, according to Cummins, the biggest initial market is expected to be in the monitoring of foodstuffs and pharmaceutical products in transit.
“Temperature, atmospheric conditions and light exposure are just the sort of thing that food and pharmaceutical companies want to measure to ensure their products have been transported safely,” he says. “Today, you can do that with a data recording module attached to a case of product. Our technology allows you to put everything you need on a single chip. It is more compact, more robust and cheaper. By replacing a module costing $10 to $15 with a tag costing $3 to $5, it now becomes possible to consider monitoring the condition of individual items.”

Ceramic layer on silicon chip allows direct sensing of temperature, humidity or even pathogens

Technology is expected to hit the market in the early part of next year

Chips could replace bulky data recording modules, such as during the transport of foodstuffs

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