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Solid-state heterostructures are the cornerstone of modern electronics. To enhance the functionality and performance of integrated circuits, the spectrum of materials used in the heterostructures is being expanded by an increasing number of compounds and elements of the periodic table. While the integration of liquids and solid-liquid interfaces into such systems would allow unique and advanced functional properties and would enable integrated nanoionic circuits, solid-state heterostructures that incorporate liquids have not been considered thus far. Here solid-state heterostructures with integrated liquids are proposed, realized, and characterized, thereby opening a vast, new phase space of materials and interfaces for integrated circuits. Devices containing tens of microscopic capacitors and field-effect transistors are fabricated by using integrated patterned NaCl aqueous solutions. This work paves the way to integrated electronic circuits that include highly integrated liquids, thus yielding a wide array of novel research and application opportunities based on microscopic solid/liquid systems.

Field-effect gating with solid dielectrics is the basis for modern electronics. Electrolyte gating, however, offers far higher polarizations. Indeed, electrolyte gating has been a breakthrough to electrically induce numerous phase transitions in solids [1,2,3]. These experiments are all done by dripping mm-size drops of the electrolytes onto the active sample. Compared to integrated circuit technology this approach seems “stone-age” to us. These drops are open to the environment, and allow only for limited purity and reproducibility. Heterostructure electronic circuits have, up to now, been comprised of solid materials only. We have opened this materials space to also include liquids. We demonstrate integrated liquid capacitors and integrated liquid field effect devices which are of equal quality or even outperform standard, bulk devices. This work will accelerate discoveries based on electrolyte gating by providing a new platform, and opens a new area to exploit liquid/solid interfaces in integrated functional devices with technological promise.

The ability to control materials properties through interface engineering is demonstrated by the appearance of conductivity at the interface of certain insulators, most famously the {001} interface of the band insulators LaAlO$_{3}$ and TiO$_{2}$-terminated SrTiO$_{3}$ (STO). Transport and other measurements in this system show a plethora of diverse physical phenomena. To better understand the interface conductivity, we used scanning superconducting quantum interference device microscopy to image the magnetic field locally generated by current in an interface. At low temperature, we found that the current flowed in conductive narrow paths oriented along the crystallographic axes, embedded in a less conductive background. The configuration of these paths changed on thermal cycling above the STO cubic-to-tetragonal structural transition temperature, implying that the local conductivity is strongly modified by the STO tetragonal domain structure. The interplay between substrate domains and the interface provides an additional mechanism for understanding and controlling the behaviour of heterostructures.

The rich array of conventional and exotic electronic properties that can be generated by oxide heterostructures is of great potential value for device applications. However, only single transistors bare of any circuit functionality have been realized from complex oxides. Here, monolithically-integrated n-type metal-oxide-semiconductor logic circuits are reported that utilize the two-dimensional electron liquid generated at the LaAlO3/SrTiO3 interface. Providing the capability to process the signals of functional oxide devices such as sensors directly on oxide chips, these results illustrate the practicability and the potential of oxide electronics.