Fabrication Of High-performance Field-effect Transistors Research Articles

Biotemplated precise assembly approach toward ultra-scaled high-performance electronics.

Structural DNA nanotechnology can be programmed into complex designer structures with molecular precision for directing a wide range of inorganic and biological materials. However, the use of DNA-templated approaches for the fabrication and performance requirements of ultra-scaled semiconductor electronics is limited by its assembly disorder and destructive interface composition. In this protocol, using carbon nanotubes (CNTs) as model semiconductors, we provide a stepwise process to build ultra-scaled, high-performance field-effect transistors (FETs) from micron-scale three-dimensional DNA templates. We apply the approach to assemble CNT arrays with uniform pitches scaled between 24.1 and 10.4 nm with yields of more than 95%, which exceeds the resolution limits of conventional lithography. To achieve highly clean CNT interfaces, we detail a rinsing-after-fixing step to remove residual DNA template and salt contaminations present around the contact and the channel regions, without modifying the alignment of the CNT arrays. The DNA-templated CNT FETs display both high on-state current (4-15 μA per CNT) and small subthreshold swing (60-100 mV per decade), which are superior to previous examples of biotemplated electronics and match the performance metrics of high-performance, silicon-based electronics. The scalable assembly of defect-free three-dimensional DNA templates requires 1 week and the CNT arrays can be synthesized within half a day. The interface engineering requires 1-2 d, while the fabrication of high-performance FET and logic gate circuits requires 2-4 d. The structural and performance characterizations of molecular-precise DNA self-assembly and high-performance electronics requires 1-2 d. The protocol is suited for users with expertise in DNA nanotechnology and semiconductor electronics.

Atomic Layer Deposition of Metal Oxides and Chalcogenides for High Performance Transistors.

Atomic layer deposition (ALD) is a deposition technique well‐suited to produce high‐quality thin film materials at the nanoscale for applications in transistors. This review comprehensively describes the latest developments in ALD of metal oxides (MOs) and chalcogenides with tunable bandgaps, compositions, and nanostructures for the fabrication of high‐performance field‐effect transistors. By ALD various n‐type and p‐type MOs, including binary and multinary semiconductors, can be deposited and applied as channel materials, transparent electrodes, or electrode interlayers for improving charge‐transport and switching properties of transistors. On the other hand, MO insulators by ALD are applied as dielectrics or protecting/encapsulating layers for enhancing device performance and stability. Metal chalcogenide semiconductors and their heterostructures made by ALD have shown great promise as novel building blocks to fabricate single channel or heterojunction materials in transistors. By correlating the device performance to the structural and chemical properties of the ALD materials, clear structure–property relations can be proposed, which can help to design better‐performing transistors. Finally, a brief concluding remark on these ALD materials and devices is presented, with insights into upcoming opportunities and challenges for future electronics and integrated applications.

Liquid-processed transition metal dichalcogenide films for field-effect transistors

Transition metal dichalcogenides (TMD) offer a great potential for optoelectronic devices. Yet large scale industrial application of unique TMD properties calls for facile processing techniques compatible with solution dispersible materials and printing technologies. In this work, we used wet processing technique to fabricate thin WS2 films and field-effect devices. The films were formed at the interface of two immiscible liquids using WS2 ethanol suspension and then were transferred onto SiO2/Si substrates. The wet processed WS2 films were found to have a high residual carbon content, which was reduced by sulfur vapor annealing as assessed by XPS. Field effect transistors (FETs) fabricated using bottom-electrode configuration exhibit Ion/Ioff ratios of 20 after annealing in the atmosphere of sulfur vapor. We conclude that TMD liquid processing can produce operational devices, but the fabrication of high-performance FETs needs to avoid organic solvents resulting in carbon contamination adversely affecting the device performance.

Biologically templated assembly of hybrid semiconducting nanomesh for high performance field effect transistors and sensors.

Delicately assembled composites of semiconducting nanomaterials and biological materials provide an attractive interface for emerging applications, such as chemical/biological sensors, wearable health monitoring devices, and therapeutic agent releasing devices. The nanostructure of composites as a channel and a sensing material plays a critical role in the performance of field effect transistors (FETs). Therefore, it is highly desirable to prepare elaborate composite that can allow the fabrication of high performance FETs and also provide high sensitivity and selectivity in detecting specific chemical/biological targets. In this work, we demonstrate that high performance FETs can be fabricated with a hydrodynamically assembled composite, a semiconducting nanomesh, of semiconducting single-walled carbon nanotubes (S-SWNTs) and a genetically engineered M13 phage to show strong binding affinity toward SWNTs. The semiconducting nanomesh enables a high on/off ratio (~104) of FETs. We also show that the threshold voltage and the channel current of the nanomesh FETs are sensitive to the change of the M13 phage surface charge. This biological gate effect of the phage enables the detection of biologically important molecules such as dopamine and bisphenol A using nanomesh-based FETs. Our results provide a new insight for the preparation of composite material platform for highly controllable bio/electronics interfaces.

Epitaxial Transfer Printing of Compound Semiconductor Nanomembranes and Device Applications

Recently, the heterogeneous integration of compound semiconductors on arbitrary substrates has attracted great interests due to their promising applications in high-performance transistors, optoelectronics, and spintronics on flexible and low-cost substrates. The heterogeneous integration of compound semiconductors on arbitrary substrates provides combined advantages of the high performance of compound semiconductors and the well-established, low-cost processing of Si, glass, and flexible substrates. However, the development of simple and efficient strategies for the heterogeneous integration of compound semiconductors on arbitrary substrates still remains a big challenge. Here, we introduce an epitaxial transfer method for the heterogeneous integration of ultrathin III-V nanomembranes on arbitrary substrates. For efficient transfer printing process, we report the fabrication of bio-inspired smart adhesive pads based on microstructured elastomers coated with thermo-responsive polymers, where the adhesion properties can be thermally controlled. In addition, we demonstrate that high-quality InAs nanoribbons are successfully integrated on Si substrates for the fabrication of high-performance field-effect transistors. Furthermore, we demonstrate heterogeneously integration of various types of compound semiconductors on arbitrary substrates for applications in spintronics and photodetectors on heterogeneous substrates.

Plasma nitridation of thin Si layers for GaAs dielectrics

10–30 Å thick Si interface control layers (ICL) were deposited on GaAs epitaxial layers on GaAs substrates. These were then nitrided by exposure to an electron cyclotron resonance nitrogen plasma for varying times. The nitride thickness is shown to increase logarithmically with time. A model based on electron tunneling is proposed to explain the results. Capacitance–voltage measurements on resulting dielectric layers showed that, under optimal conditions, results adequate to fabrication of high-performance field-effect transistors are possible. The ICL thickness cannot be reduced to zero by nitridation because of damage to the underlying GaAs.

Anomalous effects of lamp annealing in modulation-doped In0.53Ga0.47As/In0.52Al0.48As and Si-implanted In0.53Ga0.47As

The effects of pulsed halogen-lamp annealing on modulation-doped In 0.53 Ga 0.47 As/In 0.52 Al 0.48 As heterostructures and Si-implanted In 0.53 Ga 0.47 As have been studied to determine the suitabiiity of this process in the fabrication of high-performance field-effect transistors. Implantation and annealing of these materials are necessary for contact and self-aligned gate formation. Mobilities as high as 7400 cm2/ V . s are measured at 300 K in undoped molecular-beam epitaxy In-GaAs implanted with 8 × 1012cm-2 29Si+and lamp annealed at 700°C for 5 s. Anomalous overactivations (up to 120 percent) are observed in these layers When silox encapsulation is used during annealing, but the effect is absent for GaAs proximity capping. Sharp decreases in sheet-electron concentration and mobility occur in the normal modulation-doped structures for annealing temperatures > 750°C, while this trend is much smaller in the inverted structures. Arsenic loss from the In-AlAs doping layer is attributed as the main mechanism for this behavior, which makes the inverted structure more suitable for device processing. Depth profiling in the modulation-doped structures indicates that there may be serious pinchoff problems in these devices when annealed at higher temperatures due to outdiffusion of impurities from the InP substrate. Values of interdiffusion coefficients at the InGaAs/ InAIAs heterointerfaces, being reported for the first time, are almost three orders higher than those measured in the GaAs/AIAs systems.