Energy-Efficient Tunneling Field-Effect Transistors for Low-Power Device Applications: Challenges and Opportunities

Reduced subthreshold swing in a vertical tunnel FET using a low-work-function live metal strip and a low-k material at the drain

In this research paper, a vertical tunnel field-effect transistor (TFET) structure containing a live metal strip and a material with low dielectric constant is designed, and its performance metrics are analyzed in detail. Low-k SiO2 is incorporated in the channel-drain region. A live molybdenum metal strip with low work function is placed in a high-k HfO2 layer in the source-channel region. The device is examined by the parameters I off, subthreshold swing, threshold voltage, and I on/I off ratio. The introduction of a live metal strip in the dielectric layer closer to the source-channel interface results in a minimum subthreshold slope and a good I on/I off ratio. The low-k material at the drain reduces the gate-to-drain capacitance. Both the SiO2 layer and the live metal strip show excellent leakage current reduction to 1.4 × 10-17 A/μm. The design provides a subthreshold swing of 5 mV/decade, which is an excellent improvement in TFETs, an on-current of 1.00 × 10-5 A/μm, an I on/I off ratio of 7.14 × 1011, and a threshold voltage of 0.28 V.

Two-Dimensional Tunneling Memtransistor with Thin-Film Heterostructure for Low-Power Logic-in-Memory Complementary Metal-Oxide Semiconductor

With the demand for high-performance and miniaturized semiconductor devices continuously rising, the development of innovative tunneling transistors via efficient stacking methods using two-dimensional (2D) building blocks has paramount importance in the electronic industry. Hence, 2D semiconductors with atomically thin geometries hold significant promise for advancements in electronics. In this study, we introduced tunneling memtransistors with a thin-film heterostructure composed of 2D semiconducting MoS2 and WSe2. Devices with the dual function of tuning and memory operation were realized by the gate-regulated modulation of the barrier height at the heterojunction and manipulation of intrinsic defects within the exfoliated nanoflakes using solution processes. Further, our investigation revealed extensive edge defects and four distinct defect types, namely monoselenium vacancies, diselenium vacancies, tungsten vacancies, and tungsten adatoms, in the interior of electrochemically exfoliated WSe2 nanoflakes. Additionally, we constructed complementary metal-oxide semiconductor-based logic-in-memory devices with a small static power in the range of picowatts using the developed tunneling memtransistors, demonstrating a promising approach for next-generation low-power nanoelectronics.

Overcoming the Unfavorable Effects of "Boltzmann Tyranny:" Ultra-Low Subthreshold Swing in Organic Phototransistors via One-Transistor-One-Memristor Architecture

Organic phototransistors (OPTs), as photosensitive organic field-effect transistors (OFETs), have gained significant attention due to their pivotal roles in imaging, optical communication, and night vision. However, their performance is fundamentally limited by the Boltzmann distribution of charge carriers, which constrains the average subthreshold swing (SSave ) to a minimum of 60 mV/decade at room temperature. In this study, an innovative one-transistor-one-memristor (1T1R) architecture is proposed to overcome the Boltzmann limit in conventional OFETs. By replacing the source electrode in an OFET with a memristor, the 1T1R device exploits the memristor's sharp resistance state transitions to achieve an ultra-low SSave of 18 mV/decade. Consequently, the 1T1R devices demonstrate remarkable sensitivity to photo illumination, with a high specific detectivity of 3.9 × 109  cm W-1 Hz1/2 , outperforming conventional OPTs (4.9 × 104  cm W-1 Hz1/2 ) by more than four orders of magnitude. The 1T1R architecture presents a potentially universal solution for overcoming the detrimental effects of "Boltzmann tyranny," setting the stage for the development of ultra-low SSave devices in various optoelectronic applications.

The Roadmap of 2D Materials and Devices Toward Chips

Due to the constraints imposed by physical effects and performance degradation, silicon-based chip technology is facing certain limitations in sustaining the advancement of Moore's law. Two-dimensional (2D) materials have emerged as highly promising candidates for the post-Moore era, offering significant potential in domains such as integrated circuits and next-generation computing. Here, in this review, the progress of 2D semiconductors in process engineering and various electronic applications are summarized. A careful introduction of material synthesis, transistor engineering focused on device configuration, dielectric engineering, contact engineering, and material integration are given first. Then 2D transistors for certain electronic applications including digital and analog circuits, heterogeneous integration chips, and sensing circuits are discussed. Moreover, several promising applications (artificial intelligence chips and quantum chips) based on specific mechanism devices are introduced. Finally, the challenges for 2D materials encountered in achieving circuit-level or system-level applications are analyzed, and potential development pathways or roadmaps are further speculated and outlooked.

Low temperature passivation of silicon surfaces for enhanced performance of Schottky-barrier MOSFET

By using a simple device architecture along with a simple process design and a low thermal-budget of a maximum of 100 °C for passivating metal/semiconductor interfaces, a Schottky barrier MOSFET device with a low subthreshold slope of 70 mV dec-1could be developed. This device is enabled after passivation of the metal/silicon interface (found at the source/drain regions) with ultra-thin SiOxfilms, followed by the e-beam evaporation of high- quality aluminum and by using atomic-layer deposition for HfO2as a gate oxide. All of these fabrication steps were designed in a sequential process so that a gate-last recipe could minimize the defect density at the aluminum/silicon and HfO2/silicon interfaces, thus preserving the Schottky barrier height and ultimately, the outstanding performance of the transistor. This device is fully integrated into silicon after standard CMOS-compatible processing, so that it could be easily adopted into front-end-of-line or even in back-end-of-line stages of an integrated circuit, where low thermal budget is required and where its functionality could be increased by developing additional and fast logic.

Interface engineering strategy for multisource spintronic devices via TMPS4 modulation of black-phosphorus

Interface engineering is an effective strategy for significantly providing performance improvements in logic operations and information storage techniques, given the quantum effects characteristic of pristine two-dimensional ferromagnetic (FM) materials. Furthermore, the van der Waals (vdW) heterostructures enable a more efficient design of logic components. Herein, two novel designs of van der Waals heterostructures are proposed, black-phosphorus (BP)/TMPS4(TM = Cr, Fe-Mn), where the CrPS4 relies on odd and even layers for FM state - antiferromagnetic (AFM) state alternation, which is used to modulate BP with high hole mobility but no magnetism. Based on the first principles, the simulation results show that the two heterojunctions exhibit high stability, carrier mobility, and thermoelectric effects, of which the BP/CrPS4 heterojunction is specifically modulated to a type II electronic bandstructure. These two structures are applied in multi-source logic devices. The device performances show that the devices have spin Sebeck effect (SSE), perfect spin filtering effect (SFE), high extinction ratio (1347), and high thermal magnetoresistivity (1011). The above results suggest BP/TMPS4 bilayers as promising candidates for spin-based vdW devices and facilitate the future development of atomically thin magnetic information storage.

Two-Dimensional Transition Metal Dichalcogenide Tunnel Field-Effect Transistors for Biosensing Applications

Field-effect transistor (FET) biosensors based on two-dimensional (2D) materials have drawn significant attention due to their outstanding sensitivity. However, the Boltzmann distribution of electrons imposes a physical limit on the subthreshold swing (SS), and a 2D-material biosensor with sub-60 mV/dec SS has not been realized, which hinders further increase of the sensitivity of 2D-material FET biosensors. Here, we report tunnel FETs (TFETs) based on a SnSe₂/WSe₂ heterostructure and observe the tunneling effect of a 2D material in aqueous solution for the first time with an ultralow SS of 29 mV/dec. A bilayer dielectric (Al₂O₃/HfO₂) and graphene contacts, which significantly reduce the leakage current in solution and contact resistance, respectively, are crucial to the realization of the tunneling effect in solution. Then, we propose a novel biosensing method by using tunneling current as the sensing signal. The TFETs show an extremely high pH sensitivity of 895/pH due to ultralow SS, surpassing the sensitivity of FET biosensors based on a single 2D material (WSe₂) by 8-fold. Specific detection of glucose is realized, and the biosensors show a superb sensitivity (3158 A/A for 5 mM), wide sensing range (from 10^-9 to 10^-3 M), low detection limit (10^-9 M), and rapid response rate (11 s). The sensors also exhibit the ability of monitoring glucose in complex biofluid (sweat). This work provides a platform for ultrasensitive biosensing. The discovery of the tunneling effect of 2D materials in aqueous solution may stimulate further fundamental research and potential applications.

Electrical Nanobiosensors for Nucleic Acid Based Diagnostics

Recent advances in nanotechnologies have promoted the iterative updating of nucleic acid sensors. Among various sensing technologies, the electrical nanobiosensor is regarded as one of the most promising prospects to achieve rapid, precise, and point-of-care nucleic acid based diagnostics. In this Perspective, we introduce recent progresses in electrical nanobiosensors for nucleic acid detection. First, the strategies for improving detection performance are summarized, including chemical amplification and electrical amplification. Then, the detection mechanism of electrical nanobiosensors, such as electrochemical biosensors, field-effect transistors, and photoelectric enhanced biosensors, is illustrated. At the same time, their applications in cancer screening, pathogen detection, gene sequencing, and genetic disease diagnosis are introduced. Finally, challenges and future prospects in clinical application are discussed.

Performance tunability of field-effect transistors using MoS2(1-x)Se2xalloys

Ultra-thin channel materials with excellent tunability of their electronic properties are necessary for the scaling of electronic devices. Two-dimensional materials such as transition metal dichalcogenides (TMDs) are ideal candidates for this due to their layered nature and great electrostatic control. Ternary alloys of these TMDs show composition-dependent electronic structure, promising excellent tunability of their properties. Here, we systematically compare molybdenum sulphoselenide (MoS_2(1-x)Se_2x) alloys, MoS₁Se₁and MoS_0.4Se_1.6. We observe variations in strain and carrier concentration with their composition. Using them, we demonstrate n-channel field-effect transistors (FETs) with SiO₂and high-kHfO₂as gate dielectrics, and show tunability in threshold voltage, subthreshold slope (SS), drain current, and mobility. MoS₁Se₁shows better promise for low-power FETs with a minimum SS of 70 mV dec^-1, whereas MoS_0.4Se_1.6, with its higher mobility, is suitable for faster operations. Using HfO₂as gate dielectric, there is an order of magnitude reduction in interface traps and 2× improvement in mobility and drain current, compared to SiO₂. In contrast to MoS₂, the FETs on HfO₂also display enhancement-mode operation, making them better suited for CMOS applications.

Design and synthesis of a 3D flexible film electrode based on a sodium carboxymethyl cellulose–polypyrrole@reduced graphene oxide composite for supercapacitors

A novel, environmentally friendly and freestanding 3D flexible film electrode (CMC–PPy@RGO) was prepared by a simple vacuum filtration method.