Nanowire field-effect transistors (nano-FETs) are nanodevices capable of highly sensitive, label-free sensing of molecules. However, significant variations in sensitivity across devices can result from poor control over device parameters, such as nanowire diameter and the number of electrode-bridging nanowires. This paper presents a fabrication approach that uses wafer-scale nanowire contact printing for throughput and uses automated nanomanipulation for precision control of nanowire number and diameter. The process requires only one photolithography mask. Using nanowire contact printing and post-processing (i.e. nanomanipulation inside a scanning electron microscope), we are able to produce devices all with a single-nanowire and similar diameters at a speed of about 1 min per device with a success rate of 95% (n = 500). This technology represents a seamless integration of wafer-scale microfabrication and automated nanorobotic manipulation for producing nano-FET sensors with consistent response across devices.
(a) Nanomanipulation system: (1) nanomanipulator-1, (2) nanomanipulator-2, (3) nanoprobe, (4) patterned electrodes pinning nanowires. (b) The system is mounted onto and demounted from the SEM through the specimen exchange chamber. (c) Eight electrode pairs with bridging nanowires underneath.
Physical removal of unwanted nanowires. (a) The operator decides which nanowire(s) to keep. (b) The nanoprobes are lowered to the substrate surface. (c) Unwanted nanowires are severed. (d) Electrical property characterization is performed.
Automated versus Manual
For a total of 500 trials, the success rate of the system was 95%, as compared to 48.3% for manual nanomanipulation. Failure in robotic nanowire severing resulted from accidentally fracturing the target nanowire (2.2%) and the formation of an undesired nanowire network (i.e. removed ‘nano-junk’ landed on top of the target nanowire) (2.8%). Both nanowire networking and accidental target nanowire breakage were significantly lower compared to manual nanomanipulation as a direct result of precise execution of nanowire selection criteria and the high position performance of closed-loop position control.
The automated system has a speed of 1 min per device (versus 10.3 min per device for manual). The significant improvement in both success rate and efficiency resulted from automated operation that enabled specific nanowire selection and precision position control.