It's Diamond Time
The application potential for diamond is truly immense. Scientists and engineers have long understood that the fundamental properties of crystalline diamond give it the potential to outperform all other semiconductor materials for a broad range of electronic device applications. Additionally, its large bandgap, wide optical transmission window, high thermal conductivity, high structural quality, and great thermal stability make it ideal for radiation detection, high temperature electronics, and advanced optics applications including intra-cavity laser optics and x-ray diffraction optics. Additionally, the exciting properties of nitrogen-vacancy (NV) centers in diamond position it to disrupt the field of magnetic field sensing and could also enable diamond to serve as a platform material for quantum computing and quantum communications.
Why Hasn’t Diamond Taken Off Before?
Like other semiconductor materials (e.g., GaAs, InP, SiC and GaN) before it, a cost effective, large area, high quality crystalline substrate is needed to realize diamond’s full potential. For example, SiC substrates took some time to reach 2” which was required before they were taken seriously by device manufacturers. Once they entered the market, market forces supported diameter expansion all the way to today when 6” SiC is dominant and 8” SiC substrates are entering the market. However, diamond hasn’t progressed beyond 3 to 7 mm squares for over a decade (there are some exceptions but their availability is quite limited and often their quality is suboptimal). Fortunately, there is no fundamental barrier to size increase and many are working hard to realize large size high quality diamond substrates. This includes MSU which has developed several patented and proprietary technologies which can increase the size of diamond while maintaining its high quality.
Why Diamond Now?
With the immense potential for diamond as a motivation, crystal growth experts have been working for years to reduce the cost and increase the size and quality of diamond crystals. Michigan State University (MSU) and the MSU/Fraunhofer USA Center for Coatings and Diamond Technologies (CCD) are leaders in advancing the science and technology for making cost effective large area high quality diamond crystals. Great Lakes Crystal Technologies (GLCT) believes the MSU/CCD technology is ready to support an initial product offering while the company pursues further improvements in the size, quality, and cost of diamond substrates.
High Power Switching Electronics
Diamond exhibits the highest unipolar power electronics figures of merit (FOMs) in comparison to other semiconductor materials. This includes Baliga’s DC FOM, Baliga’s high frequency FOM, Johnson’s FOM, and Keye’s FOM. Diamond is the leader for these values due largely to its large critical field, large electron mobility, and in the case of Keye’s FOM, its large thermal conductivity.
For further reading see: H. Schneider, J. -. Sanchez and J. Achard, “The diamond for power electronic devices,” 2005 European Conference on Power Electronics and Applications, Dresden, 2005, pp. 9 pp.-P.9.
High Frequency Transistors
Diamond has fundamental advantages over all other semiconductors for high frequency device applications especially when high voltage and/or high power is needed. It has often been called the ultimate semiconductor because of its many superior properties over conventional semiconductors.
For further reading see: M. Kasu, “Diamond Field-effect Transistors as Microwave Power Amplifiers,” NTT Technical Review, Special Feature: Front-line Materials Research, Vol. 8 No. 8 Aug. 2010.
High Temperature Electronics
The ultra-wide bandgap and very high thermal conductivity of diamond gives it fundamental advantages over other semiconductors for high temperature electronics, which are important for automotive applications and down-hole sensing, as just two examples.
For further reading see: V. K. Khanna, “Diamond electronics for ultra-hot environments,” Chapter 10 of “Extreme-Temperature and Harsh-Environment Electronics: Physics, technology and applications,” March 2017, IOP Publishing Ltd 2017.
Magnetic Field Sensing
The nitrogen-vacancy (NV) center in diamond has atomic like electron spin properties and is sensitive to nuclear spin effects as well – and accordingly it has been researched intensely for enabling high performance magnetic field sensing.
For further reading see: J. M. Schloss, “Optimizing Nitrogen-Vacancy Diamond Magnetic Sensors and Imagers for Broadband Sensitivity,” Dissertation for Doctor of Philosophy in Physics at the Massachusetts Institute of Technology, June 2019.
The nitrogen-vacancy (NV) center in diamond has atomic like properties and has been researched intensely for its quantum properties and their application to quantum computing, quantum sensing, and quantum communications – all consider quantum technologies. Other applications are possible. According to Wikipedia, quantum technology refers to quantum computing, quantum sensors (which includes magnetic field sensing), quantum cryptography, quantum simulation, quantum metrology and quantum imaging — based on properties of quantum mechanics, especially quantum entanglement, quantum superposition and quantum tunneling.
For further reading see: J. Fedor, “Diamond based quantum technologies,” EPJ Web of Conferences 190, 01003 (2018).
High Performance Laser Optics
Single crystal diamond is an excellent material for a wide variety of laser optics, due to its very wide transmission window, its very high refractive index, and its very high thermal conductivity. It is used for simple lenses and windows and also for more advanced optical elements such as the pumped crystal in a diamond Raman laser.
For further reading see: R. J. Williams et al., “High Power Diamond Raman Lasers,” in IEEE Journal of Selected Topics in Quantum Electronics, vol. 24, no. 5, pp. 1-14, Sept.-Oct. 2018, Art no. 1602214.
X-Ray Diffraction Optics
Diamond is an excellent material for a variety of different x-ray optical elements because it has the highest thermal conductivity of any known material and a record high reflectivity in Bragg diffraction, the highest radiation hardness and elastic modulus among the X-ray optical crystals, a practical, low X-ray absorption and thermal expansion coefficients. Applications to high-heat-load monochromators for synchrotron beamlines and phase retarders for polarization control are the most common yet there are many additional applications as well.
For further reading see: S. Stoupin, “Novel diamond X-ray crystal optics for synchrotrons and X-ray free-electron lasers,” Diamond & Related Materials 49 (2014) 39–47.
Diamond possesses a number of properties including high radiation hardness, very low drift currents, and low x-ray scattering cross section that make it an excellent material for x-ray detection applications in transmission mode, including for monitoring x-ray beam conditions in free electron laser x-ray beam lines.
For further reading see: T. Zhou, et al., “Pixelated transmission-mode diamond X-ray detector,” J. Synchrotron Rad. (2015). 22, 1396-1402.