IBM paves way for wearable electronics, folding displays

SAN FRANCISCO--Bendable smartphones and electronic newspapers that can be folded up and stuff in your pocket aren't far off if IBM has its way.

The company this week described a new, low-cost technique for manufacturing silicon-based electronics on a flexible plastic substrate. While IBM acknowledges some small transistor-performance degradations in the process, the research suggests that flexible, affordable electronics can made with conventional processes at room temperature.

Comparing the approach to other one- and two-dimensional materials that have been tried for flexible electronics, "these [other] materials still have problems such as low resistance contacts, reliable gate dielectrics,"  according to Davood Shahrjerdi, research staff member with IBM's T.J. Watson Research Center. Other approaches also may have unorthodox processes or materials, or require high temperature steps during manufacture.

IBM's approach involved controlled spalling, or flaking, which it described earlier this year as "kerfless" removal of silicon, germanium and 111-V layers. In that case, IBM was using it to enable low-power photovoltaics.

The approach is oddly simple, given the device is basically fractured and the silicon substrate peeled off, after which devices are transferred to flexible plastic tape. The devices had gate lengths of less than 30 nm and a gate pitch of 100 nm.

IBM said it yielded functional SRAM cells down to VDD=0.6V, and its ring oscillators had a stage delay of 16 ps at 0.9V, which it said was the best reported for a flexible circuit.

The process is as follows: IBM began with a substrate (extremely thin SOI-ETSOI) on top of which it deposited a nickel stressor layer, about 5-6 microns thick. (The ETSOI device was fabricated on a 22-nm CMOS process using a 300-mm wafer).

Atop the stressor layer, IBM applied a flexible polyimide tape layer. At room temperature, the researchers then initiative a "stress discontinuity" at one edge and propagate the fracture front across the surface in a "mechanically controllable" manner, Shahrjerdi said.