Printer’s choice

Citation

(2009), "Printer’s choice", Sensor Review, Vol. 29 No. 4. https://doi.org/10.1108/sr.2009.08729dab.006

Printer’s choice

Article Type: News From: Sensor Review, Volume 29, Issue 4

Just as there’s a variety of candidate materials for the different parts of an electronic sensor, so too is there a broad choice of methods available for material patterning and deposition. While photolithographic processes provide are clearly the way to go as we progress down the Moore’s Law curve to the 45 nm curve and beyond. But for many low- and moderate-complexity devices, printing can do the job and is a far more cost-effective way to go. Printing equipment is inexpensive (certainly compared to the plant used in an Intel fab,) and it is relatively good when it comes to material wastage.

Traditional mask-based patterning and deposition of materials is extremely wasteful. Sequentially depositing red, green and blue phosphors through three masks, for instance, essentially wastes two-thirds of the material applied. As an additive process, printing reduces material costs, a factor that becomes more important the higher the cost of the material being used. (Certain organic inks and – more obviously gold and silver inks – used in sensors are quite expensive.) Finally, printing also has another unique advantage when it comes to sensors. Printing is effective in covering large areas very quickly, which is an important feature for manufacturing larger sensor arrays.

Almost any kind of printing approach can be used to create sensors, and several techniques are already being used in both commercial and R&D environments. Screen printing is the old stalwart from the days when “printed electronics” meant thick-film electronics, and there is a wealth of materials and accumulated expertise in this arena that could be leveraged for new-generation devices. Electrodes for electronic devices – including sensors – have in fact been screen printed for years. Screen-printed electrodes have low-unit costs in line with low-end requirements, including the production of disposable sensors. Screen printing is (for a printing technology), wasteful of materials and not generally conducive to high-volume production.

Higher volumes of printed sensors would probably be made using flexography, which has currently found a home in functional printing in the form of printing RFID antennas on labels. Gravure may also ultimately have a role in printing electronic sensors, when demand for volume production justifies its high set-up cost. Where a lot of excitement has been generated is in the ink-jet sector. Ink-jet is economical to use for small volumes and, thus, valuable for R&D and rapid prototyping; which is where a lot of the more advanced organic and printed sensor activity is right now. In addition, because ink-jet uses relatively small quantities of material, it’s very appealing for high-volume operations.

The higher the material cost, the higher the value placed on inkjet printing and alternatives that minimize materials usage. Applications requiring gold and silver will doubtlessly try to move in this direction. On the other hand, there is a real question about just how far ink-jet could scale up. Inkjet printing, further, has the added benefit of excellent registration, which can be critical for devices such as sensors that typically require precise alignment of multiple layers.

The NanoMarkets report, Printed and Organic Sensor Markets: 2007-2015 describes some of the more exciting work being done today in organic and printable electronic sensors. One example, just the tip of the iceberg, may give some impression of the type of promise printing techniques and novel materials hold for the future.

Agilent Technologies, the world’s second-largest manufacturer of nucleic acid microarrays, is making quite a splash with its chromatin immunoprecipitation-on-chip DNA microarrays, manufactured using a variation of the company’s SurePrint inkjet technology. Agilent can design and print a custom microarray at about one-tenth of the price of microarrays fabricated using traditional photolithography. According to Agilent, its printed arrays are extremely accurate and reproducible, as well as being capable of precise measurement of low levels of differential gene expression.

This example shows that printed and organic sensors are already moving well beyond devices that use printing only for electrodes. NanoMarkets believes that the sensor market represents an attractive opportunity for printed and organic electronics manufacturers in part because unlike flat-panel displays (FPDs) and RFID, this segment of electronic devices is underserved by existing manufacturers. There are many indications that the market for sensors will grow rapidly, especially in the security and medical arenas.