In today's communication systems, where frequency resources are increasingly scarce, this thin slice of quartz has become the key to ensuring signal purity. Monolithic crystal filters, with their highly ordered atomic structures and excellent physical properties, have become indispensable foundational materials in semiconductors, optoelectronics, and quantum technologies. As the demand from electric vehicles, high-performance computing (HPC), and AI-driven workloads surges, monocrystal technology is entering a new wave of development, and the global industry chain is becoming increasingly specialized. This article will guide you through the definition, working principle, characteristics, advantages, and applications of monolithic crystals.

Catalog

I. What Are Monolithic Crystals?

II. Working Principle

III. Characteristics and Advantages

IV. Applications

V. Conclusion

I. What Are Monolithic Crystals?

A monolithic crystal filter (MCF, Monolithic Crystal Filter) is an electromechanical filter produced using evaporation and photolithography techniques. It consists of a quartz wafer with metal electrodes on the surface. Unlike traditional filters made of multiple independent resonators, an MCF integrates several "poles" into a single quartz wafer, achieving miniaturization and high integration. This design not only reduces the need for external components but also significantly improves frequency stability and selectivity.

II. Working Principle

The operation of a monolithic crystal filter relies on the piezoelectric effect of quartz. When a voltage is applied to a quartz wafer, the crystal deforms mechanically; conversely, applying mechanical pressure generates an electric charge.

In an MCF, the incoming electrical signal is converted into mechanical vibrations via the inverse piezoelectric effect. These vibrations propagate through the crystal and are then converted back into an electrical signal at the output using the direct piezoelectric effect.

Quartz crystals have highly stable physical properties. Their equivalent circuit includes static capacitance C?, dynamic capacitance C?, series resistance R?, and dynamic inductance L?. When the signal frequency matches the crystal's natural frequency, it resonates, allowing the signal to pass through. Signals at other frequencies are attenuated or suppressed.

Monolithic crystal filters typically use two electrode configurations: paired electrodes or a shared ground electrode. Multiple electrode groups generate acoustic wave coupling across the wafer, enabling the filtering function.

III. Characteristics and Advantages

· High Selectivity and Low Insertion Loss: MCFs offer steep frequency responses and minimal insertion loss, ensuring high-quality signal transmission.

· Excellent Temperature Stability: Advanced quartz processing and MEMS technology provide outstanding stability across temperature variations.

· Compact Packaging: High integration results in a smaller footprint, meeting the miniaturization needs of modern electronic devices.

· High Reliability and Long Lifespan: Using high-quality materials and precise manufacturing, MCFs deliver long-term reliability even in harsh environments.

IV. Applications

Monolithic crystal filters are widely used across various industries. In the world of communications, signal purity and stability directly determine transmission quality.

Whether in remote walkie-talkie systems, base station communications, or satellite and navigation systems, crystal filters ensure precise, clear, and stable signal transmission even under demanding conditions.

Originally, crystal filters were applied in telephone communications. Today, they are extensively used for intermediate frequency selection in communication receivers and in single-sideband systems. Overall, crystal filters have become ubiquitous in navigation, fire control systems, instruments, and other electronic devices.

V. Conclusion

With the rise of 5G and IoT technologies, frequency resources are increasingly strained, and the demand for pure signals is higher than ever. Monolithic crystal filters, with their exceptional frequency selectivity and stable performance, continue to play an irreplaceable role in electronic devices. From smartphones to satellite communications, from navigation systems to industrial robots, these thin quartz wafers quietly safeguard the quality of our signals.