The fourth fundamental circuit element: principle and applications

Abstract

The relationships between four basic circuit variables—voltage (v), current (i), charge (q), and magnetic flux (ϕ)—have defined three fundamental circuit elements: resistors, capacitors, and inductors. From a viewpoint of symmetry, there is a fourth fundamental circuit element defined by the relationship between charge and magnetic flux. Historically, a device called a memristor was considered to be the fourth element, but it has caused intense controversy because a memristor is conceived based on a nonlinear i–v relationship rather than a direct q-ϕ relationship. Alternatively, a direct correlation between charge (q) and magnetic flux (ϕ) can be built up by employing the magnetoelectric (ME) effects; i.e. magnetic field control of electric polarization and electric field control of magnetization. In this review, recent progress on the principle and applications of the fourth circuit element based on ME effects is summarized. Both the fourth linear element and nonlinear memelement, termed transtor and memtranstor, respectively, have been proposed and experimentally demonstrated. A complete relational diagram of fundamental circuit elements has been constructed. A transtor with a linear ME effect can be used in a variety of applications, such as energy harvesters, tunable inductors, magnetic sensors, gyrators, transformers, etc. A memtranstor, showing a pinched hysteresis loop, has great potential in developing low-power nonvolatile electronic devices. The principle is to utilize the states of the ME coefficient α E = dE/dH, instead of resistance, magnetization, or electric polarization, to store information. Both nonvolatile memory and logic devices can be implemented by using memtranstors, which provides a route toward logic-in-memory computing systems. In addition, artificial synaptic devices that are able to mimic synaptic behaviors have also been realized using memtranstors. The fourth circuit element and memelement based on ME effects provide extra degrees of freedom to broaden circuit functionalities and develop advanced electronic devices.