Showing papers by "Benjamin C. K. Tee published in 2018"

Self-Healing Electronic Materials for a Smart and Sustainable Future.

Abstract: The survivability of living organisms relies critically on their ability to self-heal from damage in unpredictable situations and environmental variability. Such abilities are most important in external facing organs such as the mammalian skin. However, the properties of bulk elemental materials are typically unable to perform self-repair. Consequently, most conventional smart electronic devices today are not designed to repair themselves when damaged. Thus, inspired by the remarkable capability of self-healing in natural systems, smart self-healing materials are being intensively researched to mimic natural systems to have the ability to partially or completely self-repair damages inflicted on them. This exciting area of research could potentially power a sustainable and smart future.

Soft Electronically Functional Polymeric Composite Materials for a Flexible and Stretchable Digital Future.

Abstract: Flexible/stretchable electronic devices and systems are attracting great attention because they can have important applications in many areas, such as artificial intelligent (AI) robotics, brain-machine interfaces, medical devices, structural and environmental monitoring, and healthcare. In addition to the electronic performance, the electronic devices and systems should be mechanically flexible or even stretchable. Traditional electronic materials including metals and semiconductors usually have poor mechanical flexibility and very limited elasticity. Three main strategies are adopted for the development of flexible/stretchable electronic materials. One is to use organic or polymeric materials. These materials are flexible, and their elasticity can be improved through chemical modification or composition formation with plasticizers or elastomers. Another strategy is to exploit nanometer-scale materials. Many inorganic materials in nanometer sizes can have high flexibility. They can be stretchable through the composition formation with elastomers. Ionogels can be considered as the third type of materials because they can be stretchable and ionically conductive. This article provides the recent progress of soft functional materials development including intrinsically conductive polymers for flexible/stretchable electrodes, and thermoelectric conversion and polymer composites for large area, flexible stretchable electrodes, and tactile sensors.

Gigahertz Integrated Circuits Based on Complementary Black Phosphorus Transistors

Abstract: DOI: 10.1002/aelm.201800274 properties.[1–3] The utilization of 2DLMs for nanoelectronic devices offers many benefits for overcoming the scaling limits governed by Moore’s Law.[4,5] Graphene, which is attractive for its high mobility, is unsuitable for circuit application due to high off-state leakage current arising from its zero-bandgap property.[6,7] To overcome the shortcoming of graphene circuits with low on/off ratio, TMDs and more recently black phosphorus (BP), have been explored as the new channel materials for digital circuits because of their finite bandgap and superior transport properties. BP is becoming one of the promising 2DLMs for electronic applications due to its superior properties.[8] First, the unique property of BP is that it has a high mobility compared with other 2D materials, such as TMDs, thus ensuring a higher transistor current density. Besides, it shows a tunable bandgap ranging from 0.3 (bulk) to 2 eV (single layer), which enables a wide range of applications in electronics and optoelectronics. On the contrary, the main disadvantage of BP is that it is unstable and the material properties degrade quickly under ambient condition, thus an encapsulation layer, such as Al2O3 and poly (methyl methacrylate) (PMMA),[10] is necessary to protect BP from ambient degradation. Numerous field-effect transistors (FETs) based on BP[11–13] have been reported recently, in which the on/off ratio of the BP FETs is up to ≈105. In addition, BP is also demonstrated to be a superior candidate for nonvolatile memories applications.[8] However, to date, complementary 2D inverters are mostly fabricated by hybrid integration approach where two different types of 2D semiconductor are used as the channel materials. Such hybrid inverters are typically made of n-type FET, such as MoS2 n-FET,[12,14–21] and MoSe2 n-FET,[22] while typical p-type FET comprise of BP p-FET,[12,21] MoTe2 p-FET,[17] and WSe2 p-FET (Table S1, Supporting Information).[18,22] These hybrid inverters are usually achieved by either a transfer or external wiring process, which is complicated and expensive to implement for large scale manufacturing. Thus, monolithically integrated complementary inverter circuits are highly desirable and actively sought after for their simple fabrication process. Arising from the feasibility to achieve complementary doping, BP emerges as a promising material for realizing complementary integrated circuits. For instance, metal atoms have been effective in transforming pristine p-type BP into n-type conductivity,[23–26] thus allowing complementary inverters to be demonstrated on a single BP flake.[28–30] In a recent Black phosphorus (BP) has attracted enormous interest for logic applications due to its unique electronic properties. However, pristine BP exhibits predominant p-type channel conductance, which limits the realization of complementary circuits unless an effective n-type doping is found. Here, a practical approach to transform the conductivity of BP from p-type to n-type via a spatially controlled aluminum (Al) doping is proposed. Symmetrical threshold voltage for the pair of p-type and n-type BP field-effect transistors can be achieved by tuning the Al doping concentration. The complementary inverter circuit shows a clear logic inversion with a high voltage gain of up to ≈11 at a supply voltage (VDD) of 1.5 V. Simultaneously, a high noise margin of 0.27 × VDD is achieved for both low (NML) and high (NMH) input voltages, indicating excellent noise immunity. Moreover, a three-stage ring oscillator with a theoretical frequency above 1.8 GHz and microwatt level power dissipation is modeled, which shows a low propagation delay per stage. This study demonstrates a practical approach to fabricate high performance complementary integrated circuits on a homogenous BP channel material, paving the way toward complex cascaded circuits and sensor interface applications.