GaAs – your flexible friend! Aligned arrays of GaAs wires with integrated ohmic contacts generated from high‐quality, single‐crystalline wafers via photolithography and anisotropic chemical etching provide a promising class of material for transistors, Schottky diodes, logic gates (see image), and even more complex circuits on flexible plastic substrates. These devices exhibit excellent electronic and mechanical characteristics, which are both important to the emerging area of low‐cost, large‐area flexible electronics, often referred to as macroelectronics.

The combined use of GaAs wires with Ohmic contacts formed from bulk wafers, soft lithographic transfer printing techniques, and optimized device designs enables mechanically flexible transistors to be formed on low-cost plastic substrates, with individual device speeds in the gigahertz range and with high degrees of mechanical bendability. These high-speed devices incorporate materials in simple layouts that can be fabricated with modest lithographic patterning resolution and registration. This letter describes their electrical and mechanical characteristics. The results have the potential to be important to certain large-area, “macroelectronic” systems that can provide for high-speed communication and processing capabilities.

Micro/nanowires of GaAs with integrated ohmic contacts have been prepared from bulk wafers by metal deposition and patterning, high-temperature annealing, and anisotropic chemical etching. These wires provide a unique type of material for high-performance devices that can be built directly on a wide range of unusual device substrates, such as plastic or paper. In particular, transfer printing organized arrays of these wires at low temperatures onto plastic substrates yield high-quality bendable metal-semiconductor field-effect transistors. Electrical and mechanical characterization of devices on poly͑ethylene terephthalate͒ illustrates the level of performance that can be achieved. These results indicate promise for this approach to high-speed flexible circuits for emerging applications in consumer and military electronic systems.

Platinum diffusion in InAlAs was investigated utilizing a Pt∕Ti∕Pt∕Au gate contact on an In0.52Al0.48As∕In0.53Ga0.47As∕InP high-electron-mobility transistor (HEMT) structure. Capacitance-voltage measurements on large gate field-effect transistors and high-resolution cross-sectional transmission electron microscopy enabled the measurement of Pt diffusion depth with nanometer-scale accuracy. A continuous increase in Pt diffusion depth was observed at an annealing temperature of 250 °C with increasing time. After a 40 min anneal, a diffusion depth of 8 nm was measured. Such a deep Pt diffusion in a HEMT structure not only changes device parameters but also constitutes a serious reliability problem during device operation.

Enhancement-mode high electron mobility transistors (EHEMTs) were fabricated on In0.52Al0.48As/In0.53Ga0.47As heterostructures lattice-matched to InP substrates. Vertical scaling of device heterostructures was carried out to realize a positive threshold voltage with Ti/Pt/Au gates. Submicron EHEMTs utilizing Ti/Pt/Au were fabricated and their performances were compared with those of conventional EHEMTs with buried-Pt gates. DC I–V characteristics of both devices exhibited excellent pinch-off characteristics and very low output conductance. Output conductance measured for both devices showed that EHEMTs exhibit smaller kink effects than normal depletion-mode HEMTs (DHEMTs) due to the operating mode of EHEMTs with forward gate bias. EHEMTs with 0.18 µm Ti/Pt/Au gates exhibited a threshold voltage of 100 mV, peak transconductance of 810 mS/mm, and unity current-gain cut-off frequency ( fT) of 150 GHz, while those with buried-Pt gates exhibited a threshold voltage of 300 mV, peak transconductance of 880 mS/mm, and unity current-gain cut-off frequency ( fT) of 100 GHz. Studies on the thermal stabilities of the two types of gate metallization have been carried out. The Ti/Pt/Au gates exhibited better thermal stability than Pt/Ti/Pt/Au gates in terms of variation of threshold voltages and maximum transconductance values at elevated temperatures.