Flexible BiCMOS substrate with simplified process for roll-to-roll production

October 04, 2017 // By Nick Flaherty
Researchers in the US and China have developed the first flexible substrate with BiCMOS thin film transistors.

The team at the University of Wisconsin-Madison and Nanjing University have also simplified the manufacturing process for roll-to-roll production systems. 

The substrate is a transferable single crystalline Si nanomembrane (Si NM) 340nm thick on a single piece of bendable plastic substrate. The planar 1.5μm n-channel and p-channel MOSFETS and the NPN bipolar junction transistors (BJTs) were implanted into the silicon using a low cost process that was simplified by arranging the sequence of necessary ion implantation steps with carefully selected energies, doses and anneal conditions, and by combining some of the processing steps that are otherwise separately needed for all three types of transistors. 

All types of TFTs demonstrated excellent DC and radio-frequency (RF) characteristics and exhibited stable transconductance and current gain when bending, says Prof Zhenqiang (Jack) Ma, the Lynn H. Matthias Professor of Engineering and Vilas Distinguished Achievement Professor at the University of Wisconsin – Madison (shown above)

The fabrication process consists of three major steps: multiple ion implantation, transfer-printing, and microfabrication. Among these steps, the precise ion implantation and the subsequent high-temperature annealing are the key processes that enabled the flexible BiCMOS TFTs.

The physical gate length, gate width (Wg), and effective gate (channel) length (Lg) of the NMOS and PMOS TFTs are 2, 25, and 1.5μm, respectively, with outputs from 0V to 2.4V and operate from 45MHz to 20GHz.

wisned.ece.wisc.edu

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