Nanometer-Scale Ge-Based Adaptable Transistors Providing Programmable Negative Differential Resistance Enabling Multivalued Logic

Sistani, Masiar; Böckle, Raphael; Falkensteiner, David; Luong, Minh Anh; Hertog, M. den; Lugstein, Alois; Weber, Walter M.

doi:10.1021/acsnano.1c06801

Cited by 29 publications

(27 citation statements)

References 52 publications

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“…As the band-structure of Si 1−x Ge x with such high Ge contents (≥70%) is rather closer to the one of Ge than Si, [80] and still features electron conduction, the investigated Si 0.25 Ge 0.75 layer might be interesting for negative differential resistance (NDR) devices based on the electron transfer effect. [21,81,82] In contrast, the hole-gas system based on the pure Ge nanosheet confined by Si, due to the gate-tunable transparency, could be a key component for quantum computing such as gate-tunable Josephson junctions, which are an important prerequisite for gatemon or transmon qubits. [28,29] Further, the temperature sensitivity of the obtained Al-Si 1−x Ge x -Al nanosheets operated in the offregime might be very interesting for the realization of bolometers.…”

Section: Resultsmentioning

confidence: 99%

Composition Dependent Electrical Transport in Si_1−xGe_xNanosheets with Monolithic Single‐Elementary Al Contacts

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and drain electrodes in highly scaled p-channel field-effect transistors (FETs) for the realization of very-large-scale integration (VLSI) systems. [1] Despite these efforts, the continuous scaling of metaloxide-semiconductor field-effect transistors (MOSFETs) is approaching physical limits where the nature of deterministic charge carrier separation between source and drain by an energy barrier is not applicable anymore. [2,3] In the quest of overcoming scaling limitations, new lines of research arose. Device research has shifted toward new architectures, materials, and technologies to enable "More than Moore" paradigms, [4] extending the mature Si complementary metal-oxidesemiconductor (CMOS) platform. [5] In this regard, Si 1−x Ge x and Ge active regions integrated on Si platforms are promising candidates for future optoelectronic devices [6] and the realization of energy efficient steep subthreshold switches such as band-to-band tunneling transistors (TFETs), [7,8] negative capacitance Ge nanowire FETs, [9,10] and positive feedback FETs. [11] Conventionally, degenerately doped semiconductor regions in combination with thin layers made of transition-metal semiconductor alloys, such as metalsilicides [12] and metal-germanides, [13] have been used to obtain ohmic contacts to most Si 1−x Ge x and Ge based devices. Toward the achievement of ohmic contacts, pinning-free metal semiconductor contacts have been explored in Si and Ge through Si 1−x Ge x is a key material in modern complementary metal-oxide-semiconductor and bipolar devices. However, despite considerable efforts in metal-silicide and -germanide compound material systems, reliability concerns have so far hindered the implementation of metal-Si 1−x Ge x junctions that are vital for diverse emerging "More than Moore" and quantum computing paradigms. In this respect, the systematic structural and electronic properties of Al-Si 1−x Ge x heterostructures, obtained from a thermally induced exchange between ultrathin Si 1−x Ge x nanosheets and Al layers are reported. Remarkably, no intermetallic phases are found after the exchange process. Instead, abrupt, flat, and void-free junctions of high structural quality can be obtained. Interestingly, ultra-thin interfacial Si layers are formed between the metal and Si 1−x Ge x segments, explaining the morphologic stability. Integrated into omega-gated Schottky barrier transistors with the channel length being defined by the selective transformation of Si 1−x Ge x into single-elementary Al leads, a detailed analysis of the transport is conducted. In this respect, a report on a highly versatile platform with Si 1−x Ge x composition-dependent properties ranging from highly transparent contacts to distinct Schottky barriers is provided. Most notably, the presented abrupt, robust, and reliable metal-Si 1−x Ge x junctions can open up new device implementations for different types of emerging nanoelectronic, optoelectronic, and quantum devices.

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Section: Resultsmentioning

confidence: 99%

Composition Dependent Electrical Transport in Si_1−xGe_xNanosheets with Monolithic Single‐Elementary Al Contacts

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“…This is in contrast to other monolithic metal−semiconductor heterojunctions such as the Al−Ge system, which reveals a highly transparent contact for holes and a pronounced barrier for electrons. 6,44 Figure 2c shows the effect of temperature on the transfer characteristic for V D = 1 V between T = 300 and 400 K. As can be seen, a gate voltage shift and an increase of the off-current with temperature are evident, which can be attributed to the injection of thermally generated carriers over the Schottky barrier. However, no substantial increase of the on-current was observed, which is in agreement with a tunneling-dominated charge injection.…”

Section: Table 1 Calculated Diffusion Coefficients Of the Al−simentioning

confidence: 94%

“…In parallel to this development, rising computing paradigms such as the “Internet of Things” and “artificial intelligence” are demanding the design of systems with even higher computational resources. In this regard, the functional diversification of transistors constitutes alternative approaches to enable novel system concepts enhancing state-of-the-art solutions. , To overcome the scaling limitation and therefore enhance novel device concepts, it is mandatory to implement new processes and device architectures to enable “more-than-Moore” paradigms extending the mature Si complementary metal–oxide semiconductor (CMOS) platform. A major prerequisite for a large number of emerging nanoelectronic, optoelectronic, and quantum devices are reliable and reproducible metal–semiconductor junctions.…”

Section: Introductionmentioning

confidence: 99%

Monolithic and Single-Crystalline Aluminum–Silicon Heterostructures

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ACS Appl. Mater. Interfaces

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Overcoming the difficulty in the precise definition of the metal phase of metal−Si heterostructures is among the key prerequisites to enable reproducible next-generation nanoelectronic, optoelectronic, and quantum devices. Here, we report on the formation of monolithic Al−Si heterostructures obtained from both bottom-up and top-down fabricated Si nanostructures and Al contacts. This is enabled by a thermally induced Al−Si exchange reaction, which forms abrupt and void-free metal−semiconductor interfaces in contrast to their bulk counterparts. The selective and controllable transformation of Si NWs into Al provides a nanodevice fabrication platform with high-quality monolithic and single-crystalline Al contacts, revealing resistivities as low as ρ = (6.31 ± 1.17) × 10 −8 Ω m and breakdown current densities of J max = (1 ± 0.13) × 10 12 Ω m −2 . Combining transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed the composition as well as the crystalline nature of the presented Al−Si−Al heterostructures, with no intermetallic phases formed during the exchange process in contrast to state-of-the-art metal silicides. The thereof formed single-element Al contacts explain the robustness and reproducibility of the junctions. Detailed and systematic electrical characterizations carried out on back-and top-gated heterostructure devices revealed symmetric effective Schottky barriers for electrons and holes. Most importantly, fulfilling compatibility with modern complementary metal−oxide semiconductor fabrication, the proposed thermally induced Al−Si exchange reaction may give rise to the development of nextgeneration reconfigurable electronics relying on reproducible nanojunctions.

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“…However, we consider that the analogy between a transistor and a neuron is in its infancy, since the neuron has thousands of synapses connected to it and thus the advancement of solid-state intelligent matter [27] is at the beginning. Moreover, very recently, transistors such as those in this paper, able to perform different logical tasks as programmed, were referred to as adaptable or intelligent transistors [28]. Thus, our work could be an important step towards the development of artificial intelligence, which requires the fast adaptability of electron devices to various tasks.…”

Section: Discussionmentioning

confidence: 94%

Graphene/Ferroelectric (Ge-Doped HfO2) Adaptable Transistors Acting as Reconfigurable Logic Gates

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We present an array of 225 field-effect transistors (FETs), where each of them has a graphene monolayer channel grown on a 3-layer deposited stack of 22 nm control HfO2/5 nm Ge-HfO2 intermediate layer/8 nm tunnel HfO2/p-Si substrate. The intermediate layer is ferroelectric and acts as a floating gate. All transistors have two top gates, while the p-Si substrate is acting as a back gate. We show that these FETs are acting memtransistors, working as two-input reconfigurable logic gates with memory, the type of the logic gate depending only on the values of the applied gate voltages and the choice of a threshold current.

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Nanometer-Scale Ge-Based Adaptable Transistors Providing Programmable Negative Differential Resistance Enabling Multivalued Logic

Cited by 29 publications

References 52 publications

Composition Dependent Electrical Transport in Si_1−xGe_xNanosheets with Monolithic Single‐Elementary Al Contacts

Composition Dependent Electrical Transport in Si_1−xGe_xNanosheets with Monolithic Single‐Elementary Al Contacts

Monolithic and Single-Crystalline Aluminum–Silicon Heterostructures

Graphene/Ferroelectric (Ge-Doped HfO2) Adaptable Transistors Acting as Reconfigurable Logic Gates

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Nanometer-Scale Ge-Based Adaptable Transistors Providing Programmable Negative Differential Resistance Enabling Multivalued Logic

Cited by 29 publications

References 52 publications

Composition Dependent Electrical Transport in Si1−xGexNanosheets with Monolithic Single‐Elementary Al Contacts

Composition Dependent Electrical Transport in Si1−xGexNanosheets with Monolithic Single‐Elementary Al Contacts

Monolithic and Single-Crystalline Aluminum–Silicon Heterostructures

Graphene/Ferroelectric (Ge-Doped HfO2) Adaptable Transistors Acting as Reconfigurable Logic Gates

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Composition Dependent Electrical Transport in Si_1−xGe_xNanosheets with Monolithic Single‐Elementary Al Contacts

Composition Dependent Electrical Transport in Si_1−xGe_xNanosheets with Monolithic Single‐Elementary Al Contacts