Seamless integration of computing into everyday objects isn’t quite here yet, in large part because we still don’t have cheap, thin, flexible electronics. But the technology is already on a path toward ubiquity: radio frequency identification (RFID) tags are used to track goods (and, increasingly, pets and people), flexible sensors in car seats warn parents not to leave their babies behind when they go shopping, and bendable displays are on the way for e-readers. hese inherently flexible products can be mass-produced, and some can even be printed, inkjet style, to create large displays.
Made primarily from nonsilicon organic and inorganic semiconductors, including polymers and metal oxide semiconductors, flexible chips are an exciting alternative to rigid silicon circuits in simple products like photovoltaic cells and television screens, because they can be made for a fraction of the cost. But today’s flexible electronics jus t don’t perform as well as silicon chips made the old-fashioned way. For example, in February 2011 the first microprocessor made with organic semiconductors was introduced, but the 4000-transistor, 8-bit logic circuit operated at a clock frequency below 10 Hz. Compare that with the Intel 4004, introduced in 1971, which worked at 100 kilohertz and above—four orders of magnitude as fast.
A new technique for creating ultrathin silicon chips, though, could lead to many high-performance flexible applications, including displays, sensors, wireless interfaces, energy harvesting, and wearable biomedical devices. Silicon is an ideal semiconductor for such chips because its ordered structure allows for well-behaved switches that are far faster than organic alternatives.
Strangely, though, below 50 µm, silicon chips hit a sweet spot: They get more flexible and more stable. Below 10 µm, a silicon chip even becomes optically transparent, which eases the alignment of chips during assembly and allows for their use as sensors on windows and other transparent surfaces. These sub-50-µm chips are ideal for the futuristic thin-film electronic applications I described above. They’re able to bend, twist, and roll up, yet they’re as strong as stainless steel—after all, they’re still made of high-performance crystalline silicon.
And thinness enhances stackability. This is a critical attribute, given the advent of the three-dimensional integrated circuit, or 3-D IC. As chips become more complex and dense with transistors, the metal interconnects between the transistors grow longer and more convoluted. The purpose of stacking is to shorten the distance between transistors by connecting them vertically using through-silicon vias, thus speeding performance. That’s just what flash memory designers are trying to do right now.
SOURCE – IEEE Spectrum