Six decades of research on 2D materials: progress, dead ends, and new horizons

The present paper guides the reader through six decades of research on 2D materials, thereby putting special focus on the use of these materials for electronic devices. It is shown that after a slow start and only little activity over many years, since 2004 the exploration of 2D materials advanced at an enormous pace. While some of the high expectations raised in the so-called golden era of graphene did not fulfil, other electronic applications for 2D materials that originally were not on the agenda gain increasing attention now. One of the main research topics in the field of 2D materials during the early 2000s was high-performance graphene transistors. This effort, however, led to a dead end due the consequences of the missing bandgap in graphene. On the other hand, the semiconducting 2D materials show potential for different device concepts including stacked-channel 2D nanosheet MOSFETs and 2D memristors. The former may become the transistor architecture of choice at the end of the CMOS roadmap and 2D memristors represent a promising device concept for future neuromorphic computing, a type of information processing that shows great potential for artificial intelligence applications where energy efficiency is a key requirement

Failure analysis of wire bonding on strain gauge contact pads using FIB, SEM, and elemental mapping

Stacks consisting of titanium, platinum, and gold layers constitute a popular metallization system for the bond pads of semiconductor chips. Wire bonding on such layer stacks at different temperatures has extensively been investigated in the past. However, reliable information on the bondability of this metallization system after a high-temperature sintering process is still missing. When performing wire bonding after pressure sintering (at, e.g., 875 °C), bonding failures may occur that must be identified and analyzed. In the present study, a focused ion beam (FIB), scanning electron microscopy (SEM), and elemental mapping are utilized to characterize the root cause of failure. As a probable root cause, the infusion of metallization layers is found which causes an agglomerate formation at the interface of approximately 2 μm height difference on strain gauge contact pads and possibly an inhomogeneous mixing of layers as a consequence of the high-temperature sintering process. Potential treatment to tackle this agglomeration with the removal of the above-mentioned height difference during the process of contact pad structuring and alternative electrical interconnect methodologies are hereby suggested in this paper

The Role of Mobile Point Defects in Two-Dimensional Memristive Devices

Two-dimensional (2D) layered transition metal dichalcogenides (TMDCs) are promising memristive materials for neuromorphic computing systems as they could solve the problem of the excessively high energy consumption of conventional von Neumann computer architectures. Despite extensive experimental work, the underlying switching mechanisms are still not understood, impeding progress in material and device functionality. This study reveals the dominant role of mobile defects in the switching dynamics of 2D TMDC materials. The switching process is governed by the formation and annihilation dynamics of a local vacancy depletion zone. Moreover, minor changes in the interface potential barriers cause fundamentally different device behavior previously thought to originate from multiple mechanisms. The key mechanisms are identified with a charge transport model for electrons, holes, and ionic point defects, including image-charge-induced Schottky barrier lowering (SBL). The model is validated by comparing simulations to measurements for various 2D MoS$_2$-based devices, strongly corroborating the relevance of vacancies in TMDC devices and offering a new perspective on the switching mechanisms. The insights gained from this study can be used to extend the functional behavior of 2D TMDC memristive devices in future neuromorphic computing applications

Two-dimensional materials and their prospects in transistor electronics

During the past decade, two-dimensional materials have attracted incredible interest from the electronic device community. The first two-dimensional material studied in detail was graphene and, since 2007, it has intensively been explored as a material for electronic devices, in particular, transistors. While graphene transistors are still on the agenda, researchers have extended their work to two-dimensional materials beyond graphene and the number of two-dimensional materials under examination has literally exploded recently. Meanwhile several hundreds of different two-dimensional materials are known, a substantial part of them is considered useful for transistors, and experimental transistors with channels of different two-dimensional materials have been demonstrated. In spite of the rapid progress in the field, the prospects of two-dimensional transistors still remain vague and optimistic opinions face rather reserved assessments. The intention of the present paper is to shed more light on the merits and drawbacks of two-dimensional materials for transistor electronics and to add a few more facets to the ongoing discussion on the prospects of two-dimensional transistors. To this end, we compose a wish list of properties for a good transistor channel material and examine to what extent the two-dimensional materials fulfill the criteria of the list. The state-of-the-art two-dimensional transistors are reviewed and a balanced view of both the pros and cons of these devices is provided

Evolution and recent advances in RF/microwave transistors, Journal of Telecommunications and Information Technology, 2004, nr 1

Most applications for radio frequency/microwave (thereafter called RF) transistors had been military oriented in the early 1980s. Recently, this has been changed drastically due to the explosive growth of the markets for civil wireless communication systems. This paper gives an overview on the evolution, current status, and future trend of transistors used in RF electronic systems. Important background, development and major milestones leading to modern RF transistors are presented. The concept of heterostructure, a feature frequently used in RF transistors, is discussed. The different transistor types and their figures of merit are then addressed. Finally an outlook of expected future developments and applications of RF transistors is given