The Bright Future Being Created by Diamonds

The diamond is truly the king of all materials. It has many excellent properties besides its incredible hardness and high index of refraction which gives it its magical shine. The many exceptional properties of diamonds allow it to be used in a wide variety of fields from tools, to acoustic parts such as record needles, and heat dissipation components. One emerging application is use in semiconductors. As research continues, we can expect diamonds to further enrich our lives in the future.

In this article, we will introduce two exciting innovations for mobile base stations and satellite communications, both of which are essential for mobile communications. One is the diamond semiconductor power device. The second is the diamond NV-center, which is expected to have wide applicability to quantum computing*1 and high-sensitivity quantum magnetic sensors*2.

Diamond semiconductor power device

Research into semiconductor power devices*3 on diamond substrates is being conducted around the globe. Power devices are electronic components that regulate electrical power. They are used in many familiar items that support our everyday lives, such as mobile phones, cars, and electrical substations. Next-generation semiconductor materials for power devices (such as gallium nitride*5 and SiC*7) have already found widespread practical use. For example, gallium nitride is used in the Nobel Prize-winning blue LED*4 and SiC is used in power control inverters*6 of the trains and electric vehicles. With diamond semiconductor power devices, it is theoretically possible to surpass the performance of even these cutting-edge materials. For example, the figure below shows the characteristics and applications of various semiconductors, and requirements of those applications. Broadcasting stations, communications satellites, and radar devices require extremely high power output and high-speed operation, and are still equipped with vacuum tube amplifiers*8. Only diamonds, the king of materials, is expected to have the characteristics needed to meet such extreme requirements and replace vacuum tubes in such applications. Replacing vacuum tubes with semiconductors will lead to power savings, which in turn can lead to smaller size and less weight.

On April 20th, 2021, Professor Kasu Makoto of Saga University created a semiconductor power device based on a novel operating theory and announced*10 the highest ever power and voltage output of any operable transistor*9 in the world. It can be said that this was one successful step in pushing what is possible with diamond semiconductors to theoretical limits.

To put the achievement in perspective, the amount of power that the 1-inch (25.4 mm) diamond transistor shown in the upper left can regulate is equivalent to the power used by 300,000 households. It may be difficult imaging 300,000 households. There are 300,000 households in the entire prefecture of Saga, where Saga University is located.

Diamond quantum devices

The application of NV-centers of diamonds in quantum computing is also another topic of great interest. The NV-center consists of a nitrogen atom and a corresponding vacancy in the diamond lattice, as shown in the figure below, and has an independent spin (NV-). This NV-center can form a minute magnetic force (atomic spin※11) at the atomic level.

It is possible to achieve electron spin in other materials as well. However, the direction of the spin cannot be stabilized at room temperature. It is said that only diamonds can achieve electron spin at room temperature that is reliable enough for industrial application.

Research is being conducted night and day around the world to bring about innovative diamond semiconductor devices. In the next article, we will introduce Orbray’s efforts to achieve growth of large diameter diamond substrates, which are indispensable for industrializing diamond semiconductor devices and quantum devices.

Explanation of Terms

*1 Quantum computer: Conventional computers handle information as either 0s or 1s. Quantum computers can handle both states at the same time, drastically improving computing performance. If fully realized, quantum computing is expected to make great contributions to the development of new materials, solving the energy crisis, and the advancement of medical technologies.

*2 High-sensitivity quantum magnetic sensor: These sensors are able to determine the magnetism of single atoms. They are called quantum magnetic sensors because they capture changes in the quantum states of the atoms being measured.

*3 Semiconductor power device: Semiconductor is a general term for electric circuits built using semiconducting materials. Semiconductor power devices regulate electrical power. Semiconductor devices that convert light into electricity, or electricity into light, are called optical semiconductor devices. There are also semiconductor devices that handle data signals, such as the ones in your computer and other electronic devices. Semiconductor power devices are extremely energy efficient. Many recent research projects report increased milage of electric vehicles through the use of semiconductor power devices.

*4 LED: Abbreviation for light emitting diode. LEDs are semiconductor devices the emit light when powered by electricity. These lights are much more power efficient and have much longer lifetimes than conventional incandescent and fluorescent lamps. Although LEDs have existed for some time, the blue color was notoriously difficult to achieve. Dr. Akasaki, Dr. Amano, and Dr. Nakamura received the Nobel Prize in Physics in 2014 for their achievements in creating the blue LED.

*5 Galium nitride: Crystalline material made of gallium (Ga) and nitrogen (N), often abbreviated GaN. It is the main material for making LEDs. It is formed on sapphire substrate manufactured by Orbray (NAPHIATM https://www.ad-na.com/product/jewel/product/sapphire-product.html). In recent days, gallium nitride is being used not only in LEDs but in power devices for AC power supply of personal computers.

*6: Power control inverter: A device that converts direct current electricity supplied to a train into alternating current and controls the voltage and frequency of power sent to the motor to optimize performance. It can also regenerate electric power during deceleration. Optimal power control and power regeneration lead to energy savings.

*7 Crystalline material made of silicon (Si) and carbon (C). It is used in power control inverters of Yamanote Line trains.

*8 Vacuum tube amplifier: A signal amplifier that transmits high-speed, high-volume data in wireless systems, such as broadcasting ground stations, communications satellites, and radar. Developed in England in the 1950s, it still finds worldwide use today due to its high reliability.

*9 Transistor: Semiconductor power device that amplifies or switches electrical signals on/off in electronic circuits. They can be made out of silicon, SiC, GaN, diamonds, etc. Different voltages, currents, and switching speeds can be achieved depending upon the materials chosen.

*10 Saga University press release: Novel Diamond Semiconductors Operate at Highest Power Ever. (https://www.saga-u.ac.jp/koho/press/2021042021534）

*11 Electron spin: Electrons of atoms revolve around the nucleus. Magnetism is generated by the revolving electrons. For example, magnetic resonance imaging (MRI) detects the electron spins of water molecules in our bodies and create visual images of the insides of the human body.

*12 Biomarker: An indicator that quantifies some biological information of interest. It can be used to evaluate the presence or absence of disease, its progress, and effectiveness of treatment. Tumor markers that are examined in physical examinations is also one type of biomarker evaluation.