Takami Hino and his colleagues from the WPI Center for Materials Nanoarchitectonics at the National Institute for Materials Science (NIMS) in Japan have presented an analysis of new categories of nano devices and computing derived from cationic-based atomic switches.
The research is published in the Science and Technology of Advanced Materials journal.
The researchers have explained the basic methods of controlling the functioning of nanoionic atomic switches along with comprehensive illustrations of their three terminal devices and envisage a successful future for linking atomic switches with traditional silicon devices by means of ionic conductive substances.
Mechanical atomic switches driven by controlling atoms in between a conductive plane and the apex of a scanning tunneling microscope (STM) were developed in the beginning of 1990. These mechanical switches gradually led to the development of electrically controlled atomic switches, which are developed by the motion of cationic ions in electrochemical reactions and the functioning of the cationic atomic switches is controlled by the creation of a conducting route either inside or on the surface of an ionic conductor.
The recent challenge faced by the scientists in this field is the development of nanoionic switches that can be incorporated with traditional metal oxide silicon semiconductor equipment. The functioning of a basic configuration of nanoionic atomic switch includes the creation and breakdown of metallic wires of nano meter sizes by means of a solid electrochemical reaction, leading to several variations in the resistance between electrodes, i.e. the ‘on’ and ‘off’ modes.
In the review paper, the researchers have explained the manipulation of silver ions in an ionic conductor like silver sulphide. An STM apex was used to instill electrons for developing silver protuberances on the silver sulphide conductor’s surface and contraction was achieved by applying the required bias voltage in between the electrode and the STM apex. Applying positive bias a platinum layer and a silver sulphide apex led to the development of silver wires and contraction was achieved by applying a negative bias. This bipolar manipulation is essential fpr several practical applications of the nanoionic devices.
Gap-model atomic switches serve as a basic component of bipolar nanoionic devices. In the review, the researchers have offered a detailed explanation of bipolar switching by means of silver sulphide STM tips and platinum electrodes, derived from their own studies on ‘crossbar’ devices featuring a gap of 1 nm between silver sulphide tips and platinum electrodes. The authors have also highlighted the physical methods of controlling elevated speed switching at 1 MHz and also the invention that increasing bias voltage leads to exponential decrease in the switching time. They have reported that the invention of a repeatable process for developing ‘crossbar’ devices was a significant breakthrough, which led to the first revelation of nanoionic circuits like logic gates.
In order to explain the practical applications of atomic switches the researchers enunciated illustrations of sophisticated atomic switches like gapless-type devices featuring metal/ionic conductor/metal structures, in which one the metal is electrochemically inactive and the other one electrochemically active. Gapless atomic switches also serve as memory resistors (also termed as ‘memristors’). Memory resistors are passive two terminal multi-state memory devices, in which the dimensions of the nanowire projections control the functional attributes.
Three terminal devices like structures featuring a solid copper sulphide electrolyte are other innovative atomic switches. In this type, the copper gate-electrode manipulates the creation of a copper bridge between a platinum electrode (source) and copper electrode (drain). The other advanced atomic switches are photo-aided atomic switches that do not need nanogaps, and optical irradiation of a photoconductive material situated in between the anion and electron conducting electrode and a counter metal electrode enables the creation of nanowire projections. This type of atomic switches are programmable that could be utilized in erasable programmable read-only memory (EPROM).
The researchers have also explained the learning capabilities of atomic switches in single nanoionic devices with short-term and long-term memories, field programmable gate arrays incorporated with CMOS devices and two terminal atomic switch logic gates. The review includes 20 figures and 77 references and offers valuable latest data for both beginners and professionals in this field.