bf iedm flexible plastic
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
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
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,