Dielectrophoresis and Chemically Mediated Directed Self-Assembly of Micrometer-Scale Three-Terminal Metal Oxide Semiconductor Field-Effect Transistors

✍ Scribed by S. W. Lee; R. Bashir

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 471 KB
• Volume: 17
• Category: Article
• ISSN: 0935-9648
• DOI: 10.1002/adma.200501048

✦ Synopsis

Directed self-assembly techniques, such as fluidic self-assembly, [1][2][3] liquid-solder-based self-assembly, [4,5] self-assembly using capillary forces in fluid, [6,7] and shape-and-solder-directed self-assembly, [8,9] has been studied by many researchers in recent years in order to implement micro-and nanoscale electronic devices and to integrate heterogeneous materials and devices. These self-assembled systems can be used to construct hybrid devices with good electronic properties by using high-quality material to fabricate the initial device and then assembling these devices on other substrates. However, many challenges still remain. All studies to date have been demonstrated using devices or blocks containing devices that are 50 lm or larger. As the size of the devices is reduced, the efficiency and position precision is also reduced. We demonstrate here, for the first time, dielectrophoresis (DEP) [10] and chemically mediated fluidic self-assembly of individual three-terminal silicon metal oxide semiconductor field-effect transistors (MOSFETs) on a patterned substrate. Moreover, currentvoltage (I-V) characteristics of the assembled MOSFETs were measured after the solution was evaporated and the contacts were annealed.

Single-crystal silicon MOSFETs of 2 lm width, 15 lm length, and 1.3 lm thickness with a polycrystalline silicon gate, silicon nitride spacers at the end of the gate stack, and gold source-drain contacts were designed and fabricated on a bond and etched back silicon-on-insulator (BESOI) wafer as shown in Figure 1a. (The fabrication of the MOSFET is described in the Experimental.) The MOSFETs were successfully released from the host BESOI wafer as described earlier. [11,12] Buffered hydrofluoric acid (BHF) was used to partially etch the buried oxide so that the oxide pillar held the device on the BESOI wafer. The wafer was transferred into deionized (DI) water with 0.05 % Tween 20, and the beaker was placed in an ultrasonic agitator. After the pillars were broken by ultrasonic agitation, the MOSFETs were released into solution, as shown in Figures 1b,c. Meanwhile, the assembly substrates (non-functionalized or functionalized with selfassembled monolayers (SAMs)) were formed on oxidized silicon wafers (which could be any substrate capable of sustaining low-temperature processes steps). A gold film (700 Å) with a chromium adhesion layer (300 Å) was deposited on the assembly substrate. Functionalized electrodes were formed using SAMs of 1,9-nonanedithiol (HS(CH 2 ) 9 SH) by incubating the substrate in the solution for 24 h.