Diamond Acoustic Sensor

Diamond Acoustic Sensor

Diamond is widely recognized as the ultimate thermal management material, but its exceptional physical properties extend far beyond heat dissipation. With an acoustic velocity exceeding 10,000 m/s, extremely high mechanical stiffness, low acoustic loss, excellent chemical resistance, and thermal conductivity above 2,000 W/m·K, diamond provides a unique platform for high-frequency acoustic sensing.

One promising architecture is the High-overtone Bulk Acoustic Resonator (HBAR). In a diamond HBAR, a piezoelectric thin film such as AlN or AlScN is integrated with a single-crystal diamond substrate. A microwave electrical signal excites bulk acoustic waves through the piezoelectric layer. These waves propagate into the diamond and repeatedly reflect between its parallel surfaces, generating high-order acoustic resonances at GHz frequencies.

When the diamond surface is exposed to a liquid, the acoustic boundary condition changes according to the liquid's acoustic properties. This interaction modifies the resonator's resonance characteristics, including its reflection coefficient, resonance amplitude, and quality factor (Q). By monitoring these changes, the sensor can determine parameters such as acoustic impedance and acoustic loss.

Why Diamond?

The key advantage of diamond is its ability to combine high acoustic velocity with extremely low mechanical loss. A higher acoustic velocity enables higher resonance frequencies for a given substrate thickness, while low acoustic attenuation allows the resonator to maintain a high Q factor. Diamond's exceptional thermal conductivity also helps dissipate microwave and acoustic losses, improving frequency stability and power handling.

Recent demonstrations of diamond-based microwave HBAR sensors have achieved resonance frequencies around 5 GHz with Q values exceeding 10,000, while requiring only milligram-scale liquid samples. Such performance illustrates the potential of diamond as a high-frequency acoustic sensing platform rather than simply a thermal substrate.

From Liquid Properties to Chemical Process Monitoring

Unlike conventional electrical or electrochemical sensors, diamond acoustic sensors do not necessarily require direct electrical interaction with the liquid. The sensing interface can be the exposed diamond surface, while the piezoelectric transducer and electrodes remain isolated from the environment.

This architecture provides several advantages:

• GHz-frequency operation for high-resolution acoustic measurements

• High Q-factor for improved frequency and amplitude sensitivity

• Small sample volume, potentially down to milligram-scale quantities

• Chemically robust sensing surface based on diamond

• Reusable sensor structure with simplified surface cleaning

• Non-electrochemical measurement, enabling characterization of liquids that are difficult to measure electrically

The same acoustic platform can also be extended beyond liquid-property measurement. Changes in the mass, mechanical properties, or acoustic boundary conditions at the diamond surface can be used to monitor thin-film deposition, oxidation, chemical reactions, and other surface processes.

Diamond + AlScN: A High-Frequency Sensing Platform

The development of high-performance AlScN piezoelectric films further expands the potential of diamond acoustic sensors. Scandium alloying can substantially enhance the piezoelectric response of AlN, providing stronger electromechanical coupling while maintaining compatibility with high-frequency BAW architectures.

The combination of AlScN transduction + diamond acoustic propagation therefore creates a powerful material platform:

AlScN → efficient electrical-to-acoustic conversion
Diamond → ultra-high-speed, low-loss acoustic propagation
Diamond surface → robust sensing interface

This materials combination opens a pathway toward acoustic sensors operating well beyond conventional MHz-range technologies and into the multi-GHz regime.

Beyond Thermal Management

The significance of Diamond Acoustic Sensor technology is broader than a new type of liquid sensor. It demonstrates a different way of utilizing diamond's extraordinary material properties.

Diamond can simultaneously provide thermal management, mechanical stiffness, acoustic performance, chemical stability, and high-frequency compatibility within a single platform.

For next-generation sensing systems, this creates opportunities in liquid characterization, industrial process monitoring, chemical sensing, environmental analysis, high-frequency MEMS, and advanced semiconductor and RF systems.

Diamond is no longer only a material for moving heat away from high-power devices. It can also become the medium through which high-frequency acoustic information is generated, transmitted, and detected.

Diamond Acoustic Sensor: turning the exceptional acoustic properties of diamond into a new sensing dimension.