Functional Microstructures by Self-Assembly - Molecular Self-Assembly: Advances and Applications - page 403

microscale components, including single-crystal silicon field-
effect transistors (FETs), diffusion resistors, and microscale light
emitting diodes ( -LEDs). All of these tasks have been carried out on

unconventional plastic substrates, as discussed below.
In 2006, our group published a paper on successful assembly of
silicon FETs and diffusion resistors onto a plastic substrate. In this
review, we achieved a site occupation efficiency of 97% in 25 min,
for 100

µ

m circular components assembling onto 10,000 binding
site templates. The result is shown in Fig. 12.12. The functionality
of the application was demonstrated by placing free-standing n-type
FETs onto a plastic substrate to create active electronic circuitry.

µ

Figure 12.12 High yield self-assembly of circular, single-crystal silicon

elements onto a flexible plastic template. (a) The completed
flexible template containing 10,000 binding sites; (b) the
enlarged image of about 2000 binding sites. Reprinted from
Ref. [9]. Copyright 2006 National Academy of Sciences, USA.

In order to extend the application into the optoelectronic domain,
we have reported the self-assembly of microscale compound
semiconductor -LEDs onto plastic substrates using a one-step

process [10]. The self-assembly process is similar as before. The
plastic template and

µ

µ

-LEDs were fabricated separately and released
into a liquid medium. Fluid flow activated -LEDs to move and

gravity made them fall into complementarily shaped binding sites.
The low melting point alloys at the bottom of binding sites wetted
the metal pads on

µ

µ

-LEDs and formed connection between

µ

-LEDs

and the template circuit. The process is shown in Fig. 12.13.