Innovative Surface Acoustic Wave Device for Ramping Up Output Frequencies

In the “internet of things” network adopted at present, devices fundamentally connect at high speeds over short ranges, a setting where surface acoustic wave (SAW) devices have shown promise for many years now, leading to reduction in the size of smartphone.

However, to achieve ever higher speeds, SAW devices ought to function at higher frequencies, which restricts output power and can affect overall performance. An innovative SAW device seems to offer a way forward for these devices to achieve even greater frequencies.

A research team from China has developed a SAW device with the potential to attain frequencies six times greater than a majority of the prevalent devices. Incorporating interdigital transducers (IDTs) embedded on a layer of combined diamond and aluminum nitride, the device developed by the researchers could also considerably scale up the output. The outcomes of the study have been reported this week in Applied Physics Letters published by AIP Publishing.

We have found the acoustic field distribution is quite different for the embedded and conventional electrode structures. Based on the numerical simulation analysis and experimental testing results, we found that the embedded structures bring two benefits: higher frequency and higher output power.

Jinying Zhang, Author of the Paper

In order to transmit a high-frequency signal, surface acoustic wave devices transform electric energy into acoustic energy. This is usually performed using piezoelectric materials, which have the potential to change shape upon applying an electric voltage. IDT electrodes are usually positioned on top of piezoelectric materials to carry out this transformation.

Scaling up the operational frequency of IDTs, as well as the overall signal speed, has seemed to be challenging. According to Zhang, majority of the prevalent SAW devices attain the highest speed at a frequency of nearly 3 GHz. However, in general, devices that are 10 times faster can be prospectively achieved. Yet, higher frequencies mandate more power to compensate for the signal loss, and consequently, certain aspects of the IDTs have to be very small. Although a 30 GHz device has the potential to transmit a signal at higher speeds, its operational range gets restricted.

The major challenge is still the fabrication of the IDTs with such small feature sizes. Although we made a lot of efforts, there are still small gaps between the side walls of the electrodes and the piezoelectric materials.

Jinying Zhang

In order to be certain that the transducers have the appropriate feature size, Zhang and his colleagues required a material that had high acoustic velocity, for example, diamond. Then, they coupled diamond, which does not change in shape much upon applying electric voltage, with aluminum nitride (a piezoelectric material), and implanted the IDT within their new SAW device.

The resultant device functioned at a frequency of 17.7 GHz and enhanced the power output by 10% as against traditional devices adopting SAWs.

“The part which surprised us most is that the acoustic field distribution is quite different for the embedded and conventional electrode structures,” stated Zhang. “We had no idea at all about it before.”

Zhang believes that this study will pave the way for the application of SAW devices in monolithic microwave integrated circuits (MMICs), which are inexpensive, high-bandwidth integrated circuits being used in a range of high-speed communications, for example, cell phones.