In this issue we have endeavored to answer the question, “Whither oxide electronics?” This issue provides a framework and perspective on the progress in the field of oxide electronics over the past several decades, as well as the challenges and opportunities in the years to come. Building on the foundations laid by the pioneers in the materials community and spurred by the discovery of high-temperature superconductivity, there has been both tremendous progress in understanding the complex science of oxide electronic materials and the discovery of other fascinating new phenomena, including colossal magnetoresistance, multiferrocity, and two-dimensional electron gases in correlated oxide systems. Thin-film heterostructures provide a pathway to create novel devices and combinations of physical phenomena. Indeed, the ability to synthesize and control oxide heterostructures using sophisticated deposition techniques has become a key enabler of the recent advances in this field. These oxides are beginning to enter mainstream products because of their higher performance, for example, ferroelectric memories and oxides with high dielectric constant for computers that run at higher speed and use less power.

This year marks a major materials milestone in the makeup of silicon-based field-effect transistors: in the microprocessors produced by leading manufacturers, the SiO2 gate dielectric is being replaced by a hafnium-based dielectric. The incredible electronic properties of the SiO2/silicon interface are the reason that silicon has dominated the semiconductor industry and helped it grow to over $250 billion in annual sales, as reported by the Semiconductor Industry Association (SIA), San Jose, CA. The shrinkage of transistor dimensions (Moore's law) has led to tremendous improvements in circuit speed and computer performance. At the same time, however, it has also led to exponential growth in the static power consumption of transistors due to quantum mechanical tunneling through an ever-thinner SiO2 gate dielectric. This has spurred an intensive effort to find an alternative to SiO2 with a higher dielectric constant (K) to temper this exploding power consumption. This article reviews the high-K materials revolution that is enabling Moore's law to continue beyond SiO2.

Two-dimensional electron gases (2DEGs) based on conventional semiconductors such as Si or GaAs have played a pivotal role in fundamental science and technology. The high mobilities achieved in 2DEGs enabled the discovery of the integer and fractional quantum Hall effects and are exploited in high-electron-mobility transistors. Recent work has shown that 2DEGs can also exist at oxide interfaces. These electron gases typically result from reconstruction of the complex electronic structure of the oxides, so that the electronic behavior of the interfaces can differ from the behavior of the bulk. Reports on magnetism and superconductivity in oxide 2DEGs illustrate their capability to encompass phenomena not shown by interfaces in conventional semiconductors. This article reviews the status and prospects of oxide 2DEGs.

In complex transition-metal oxides, the interactions between the electronic spins, charges, and orbitals produce a rich variety of electronic phases. The competition and/or cooperation among these correlated-electron phases can lead to the emergence of surprising electronic phenomena and functionalities and form the basis for a new type of electronics.

In this article, we review current research efforts to control the magnetic behavior of complex oxide thin films using electric fields. After providing fundamental definitions of magnetoelectric response, we survey materials, architectures, and mechanisms that exhibit promise for such electric-field control of magnetism. Finally, we mention ideas for future research and discuss prospects for the field.

Magnetism in oxides was thought to be well-understood in terms of localized magnetic moments and double-exchange or superexchange rules. This understanding was shaken by the publication of an article in 2001 stating that thin films of anatase TiO2 with only 7 at.% Co substitution had a Curie point in excess of 400 K [Matsumoto et al., Science291, 854 (2001)]. Room-temperature ferromagnetism had previously been predicted for p-type ZnO with 5 at.% Mn [Dietl et al., Science287, 1019 (2000)]. A flood of reports of thin films and nanoparticles of new oxide “dilute magnetic semiconductors” (DMSs) followed, and high-temperature ferromagnetism has been reported for other systems with no 3dcations. The expectation that these materials would find applications in spintronics motivated research in this area. Unfortunately, the data are plagued by instability and a lack of reproducibility. In many cases, the ferromagnetism can be explained by uncontrolled secondary phases; it is absent in well-crystallized films and bulk material. However, it appears that some form of high-temperature ferromagnetism can result from defects present in the oxide films [Coey, Curr. Opin. Solid State Mater. Sci.10, 83 (2007); Chambers, Surf. Sci. Rep.61, 345 (2006)], although they are not DMSs as originally envisaged.

This article provides a review of materials and devices of wide-bandgap oxide semiconductors based on ZnO, highlighting the nature of the chemical bond. The electronic structures of these materials are very different from those of conventional covalently bonded semiconductors, owing to the ionic nature of the chemical bonds. Therefore, one needs to design and optimize fabrication processes and structures of active devices containing such materials, taking into account the peculiar defect formation mechanisms. A variety of active devices that have clear advantages over the conventional ones have been demonstrated, for example, ultraviolet light-emitting diodes, quantum Hall devices, and transparent and flexible thin-film transistors with high electron mobility, paving the way for future applications. The reasons behind the successes identify future challenges in research on oxide semiconductors.