A compute-in-memory macro that is based on complementary metal–oxide–semiconductor (CMOS) technology and resistive random-access memory can be used for precise and efficient neural network implementation. The photograph on the cover shows the compute-in-memory chip (top), interconnect breakout boards (middle) and the field-programmable gate array (FPGA) control board (bottom).

See Hung et al.

A wireless radiofrequency power supply can be used to drive a flapping-wing aerial vehicle. The photograph on the cover shows the insect-scale robot, which has a mass of only 1.8 g.

See Ozaki et al.

Graphene can be doped to high carrier densities via charge transfer from a neighbouring monolayer of tungsten oxyselenide, which is created by oxidizing a layer of tungsten diselenide. The optical microscopy image on the cover shows two silicon nitride microring resonators, with the top resonator incorporating the doped graphene as a transparent electrode.

See Choi et al.

Multidirectional currents on conductive surfaces built into the walls of a room can generate widely distributed magnetic field patterns that wirelessly power electronic devices located anywhere in the room. The long-exposure photograph on the cover shows the path a wirelessly powered red light-emitting diode (LED) took as it was carried through a test room for the wireless power transfer technique.

See Sasatani et al.

Particle-based thermoelectric inks can be written into complex three-dimensional thermoelectric architectures using a 3D printing process, creating devices that could generate power from minimal heat flow or act as coolers in integrated systems. The computer-generated image on the cover illustrates the direct ink writing of a microscale thermoelectric device on an integrated circuit.

See Kim et al.

In an approach that mimics the capabilities of the human visual system, an organic transistor based on two complementary bulk heterojunctions can exhibit visual adaptation behaviour that is light intensity dependent. The photograph on the cover shows an array of the devices on a flexible substrate and attached to a transparent marble.

See He et al. and News & Views by Jie et al.

High-speed transistors that are based on arrays of aligned carbon nanotubes could potentially be scaled for operation in millimetre-wave and terahertz frequencies. The cover shows a scanning electron microscopy image of a six-finger nanotube transistor that is fabricated on a silicon wafer and can be used to build a radiofrequency amplifier.

See Shi et al.

An electro-optic phase modulator based on titanium-doped lithium niobate can be used to readout a superconducting electromechanical device operating at a temperature of 15 mK. The computer-generated image on the cover shows a gold-plated dilution fridge that can be used to cool superconducting circuits; laser beams have been incorporated into the image to highlight the optical nature of the new readout scheme.

See Youssefi et al. and News & Views by Usami et al.

Stretchable sensors that are made from two conductive fibres in a double helical structure and with a hollow core can be directly sutured to connective tissues to wirelessly monitor strain. The computer-generated image on the cover illustrates a stretchable strain sensor with a double helical turn density of three turns per centimetre and a hollow core diameter of 500 micrometres.

See Lee et al.

Fibres with a coaxial structure in which conductive stainless-steel threads are coated with a piezoresistive nanocomposite can be machine knitted into wearable garments — including gloves, vests and socks — that can be used to monitor and recognize tactile interactions. The optical image on the cover shows a stainless-steel thread (top), coaxial piezoresistive fibre (middle) and acrylic knitting yarn (bottom).

See Luo et al. and News & Views by Chen et al.

With the help of conformable electrodes, a Venus flytrap can be converted into an on-demand actuator that can be wirelessly controlled via a smartphone and has a power input of only 10−5 W. The cover shows a photograph of the conformable electrodes on the epidermis of open and closed Venus flytraps.

See Li et al. and News & Views by Volkov

For our 2021 technology of the year, we explore the impact of the coronavirus pandemic on digital technology. The illustration on the cover highlights one technology — digital contact tracing — that has been used to try to slow the spread of the virus.

See Editorial