Self-Aligned van der Waals Heterojunction Diodes and Transistors

Abstract

A general self-aligned fabrication scheme is reported here for a diverse class of electronic devices based on van der Waals materials and heterojunctions. In particular, self-alignment enables the fabrication of source-gated transistors in monolayer MoS2 with near-ideal current saturation characteristics and channel lengths down to 135 nm. Furthermore, self-alignment of van der Waals p-n heterojunction diodes achieves complete electrostatic control of both the p-type and n-type constituent semiconductors in a dual-gated geometry, resulting in gate-tunable mean and variance of anti-ambipolar Gaussian characteristics. Through finite-element device simulations, the operating principles of source-gated transistors and dual-gated anti-ambipolar devices are elucidated, thus providing design rules for additional devices that employ self-aligned geometries. 2For example, the versatility of this scheme is demonstrated via contact-doped MoS2 homojunction diodes and mixed-dimensional heterojunctions based on organic semiconductors. The scalability of this approach is also shown by fabricating self-aligned short-channel transistors with subdiffraction channel lengths in the range of 150 nm to 800 nm using photolithography on large-area MoS2 films grown by chemical vapor deposition. Overall, this self-aligned fabrication method represents an important step towards the scalable integration of van der Waals heterojunction devices into more sophisticated circuits and systems. TOC IMAGE 3Parallel self-aligned fabrication methods in modern silicon-based microelectronics have enabled sub-lithographic registration between processing steps, ultimately facilitating substantial advances in circuit complexity over the past few decades. 1 In contrast, while two-dimensional (2D) materials have shown significant potential for digital and analog electronics due to their high mobilities, ultrathin geometry, and broad range of permutations in van der Waals heterojunctions (vdWHs), 2-9 2D material devices have not yet exploited parallel self-aligned fabrication to achieve both short channels and large area fabrication. Thus far, short-channel 2D material transistors and vdWHs have been achieved using serial processing methods such as electron-beam lithography or mechanical placement on nanotube or nanowire gates. 5,10,11 Similarly, the relative alignment of different layers in vdWHs has been inhibited by the diffraction-limited resolution of transfer and alignment methods. Here, we overcome these limitations by introducing a self-aligned processing methodology that enables the fabrication of 2D material transistors with channel lengths below 150 nm with minimal short-channel effects and improved current saturation, as demonstrated with monolayer MoS2. These self-aligned transistors show the highest output resistance at the lowest channel length reported for a 2D material, which is of interest for high-frequency current amplifiers and mixers. In vdWHs based on black phosphorus (BP) and MoS2, this self-aligned approach allows dual-gate ...

Spiking neurons from tunable Gaussian heterojunction transistors

“…The GHeTs were first characterized by biasing the bottom and top gates independently with the source voltage (V S ) grounded. Figure 2a shows selected output curves corresponding to different top gate voltages (V TG ) for V BG = 0 V. The top gate modulates the output response of the GHeT from a rectifying diode at V TG = -6 V (orange) to an inverted polarity rectifying diode at V TG = 6 V (purple) due to band-to-band tunneling between the MoS 2 and CNTs as has been previously reported 37,41,45 . Supplementary Fig.…”

“…Solution-processed CNTs were the ideal candidate for the second semiconducting material because of their p-type/ambipolar characteristics, ability to conform over arbitrary nonplanar surfaces, and desired band alignment with MoS 2 28,41 . Therefore, a recently reported self-alignment method 37 was adapted to large-area photolithography to enable the fabrication of dual-gated GHeTs from MoS 2 and CNTs. As shown in Fig.…”

“…In particular, the incorporation of atomically thin semiconducting materials into gate-tunable p-n heterojunctions results in an antiambipolar response with Gaussian transfer curves [28][29][30][31][32][33][34][35][36][37][38] . While this behavior has been used for analog signal processing 37,39 , logic devices 30,35,38 , and photodetectors 28,32,34 , the single-gated geometries used previously do not provide sufficient control over the Gaussian current-voltage characteristic to enable efficient neuromorphic functionality. Here, we report the scalable fabrication of dual-gated Gaussian heterojunction transistors (GHeTs) based on mixed-dimensional van der Waals heterojunctions 40 consisting of monolayer molybdenum disulfide (MoS 2 ) grown via chemical vapor deposition (CVD) and solution-processed semiconducting single-walled carbon nanotubes (CNTs).…”

Compact Source-Gated Transistor Analog Circuits for Ubiquitous Sensors

“…1a and 1b show cross-sections of two SGTs with sourcegate overlap S and source-drain separation, d. (SGTs ordinarily do not use the more general notation L for sourcedrain gap, as their effective channel length varies with applied bias in a manner additional to channel length shortening in FETs, hence the distinct terminology). SGTs have been explored in a variety of materials including amorphous [29] and polysilicon [23], [25], [28], [30], ZnO [31], InGaZnO (IGZO) [26], [32], organics [33], MoS2 [34] and semimetals [26], with several means of engineering an energy barrier at the source, including Schottky contacts ( Fig. 1a), bulk unipolar contacts [35], [36], or incorporating a tunnel barrier [32] (Fig.…”

Negative Transconductance Heterojunction Organic Transistors and their Application to Full‐Swing Ternary Circuits

“…Recently, heterojunction transistors (H‐TRs) based on various semiconductor materials have been studied for MVL implementation utilizing their negative differential resistance or transconductance characteristics. The materials for H‐TRs include transition metal dichalcogenides (TMDs), organic semiconductors, graphene, and hybrid material combinations, including carbon nanotube (CNT)‐molybdenum disulfide (MoS 2 ), organic‐MoS 2 , and indium gallium zinc oxide (IGZO)‐CNT …”