基于高声速材料金刚石的17.7 GHz声表面波器件

实验室合成钻石 2018-11-07 14:07:42

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基于高声速材料金刚石的17.7 GHz声表面波器件

在今天的“物联网”中,设备在高速上主要连接短距离的设备,在这种环境下,表面声波(SAW)设备多年来已经显示出了一定的前景,例如智能手机的体积缩小。然而,为了获得更快的速度,设备需要在更高的频率下运行,这限制了输出功率,并且会降低整体性能。一种新的SAW装置可以为这些设备提供通向更高频率的路径。



中国的研究团队展示了一种能达到比大多数当前设备高六倍频率的声表面波装置。在氮化铝和金刚石的复合层上嵌入叉指换能器(IDT),该团队的设备也能显著提高输出量。他们的研究结果发表在本周的《应用物理快报》(Applied Physics Letters)上。


该论文的作者之一,张金英说:“我们发现,在嵌入式和传统电极结构中,声场分布是完全不同的。” “基于数值模拟分析和实验测试结果,我们发现嵌入式结构有两大优点:频率更高、输出功率更高。”


声表面波器件通过将电能转换为声能来传输高频信号。这通常是用压电材料来完成的,压电材料可以在电压下改变形状。IDT电极通常放置在压电材料的顶部来执行这种转换。提高IDTS的运行频率和整体的信号速度,已经被证实是很困难的。目前大多数的设备都以大约3千兆赫的频率出现,但原则上,有可能制造出速度快10倍的设备。然而,更高的频率需要更多的功率来克服信号的损失,并且,IDTs的某些特性需要变得越来越小。虽然一个30 GHz的设备可以更快地传输信号,但它的操作范围是有限的。


“主要的挑战仍然是制造这些小尺寸的叉指换能器,”张金英说。“虽然我们做了很多努力,但在电极的侧壁与压电材料之间仍有很小的间隙。”



为了确保传感器具有合适的尺寸,研究团队需要一种具有高声速的材料——金刚石。然后,他们将金刚石与压电材料氮化铝结合在一起,这种材料的形状随电压变化很小,之后将IDT嵌入到他们的新的SAW设备中。这一装置的运行频率为17.7 GHz,与传统的使用SAW的设备相比,功率输出提高了10%。


张金英说:“最让我们惊讶的是,对于嵌入式电极结构和传统电极结构,声场分布有很大的不同。然而,我们以前根本不知道这件事。”她希望这项研究能让人们看到SAW设备在单片微波集成电路(MMICs)中使用,低成本、高带宽的集成电路,应用在各种高速通信,比如手机。



 金刚石是自然界存在的特殊材料之一,具有最高的硬度、低摩擦系数、高弹性模量、高热导、高绝缘、宽能隙、高的声传播速率以及良好的化学稳定性等,如下表。虽然天然金刚石具有这些独一无二的特性,但是它们一直仅仅是以宝石的形式存在,其性质的多变性和稀有性极大地限制了其应用。而洛阳誉芯金刚石制备的CVD金刚石膜将这些优异的物理化学性能集一身,且成本较天然金刚石低,能够制备各种几何形状,在电子、光学、机械等工业领域有广泛的应用前景。



Acoustic Device Makes Piezoelectrics 

Sing to a Different tune

In today's "internet of things," devices connect primarily over short ranges at high speeds, an environment in which surface acoustic wave (SAW) devices have shown promise for years, resulting in the shrinking size of your smartphone. To obtain ever faster speeds, however, SAW devices need to operate at higher frequencies, which limits output power and can deteriorate overall performance. A new SAW device looks to provide a path forward for these devices to reach even higher frequencies.



A team of researchers in China has demonstrated a SAW device that can achieve frequencies six times higher than most current devices. With embedded interdigital transducers (IDTs) on a layer of combined aluminum nitride and diamond, the team's device was also able to boost output significantly. Their results are published this week in Applied Physics Letters.


"We have found the acoustic field distribution is quite different for the embedded and conventional electrode structures," said Jinying Zhang, one of the paper's authors. "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."


Surface acoustic wave devices transmit a high-frequency signal by converting electric energy to acoustic energy. This is often done with piezoelectric materials, which are able to change shape in the presence of an electric voltage. IDT electrodes are typically placed on top of piezoelectric materials to perform this conversion.


Ramping up the operational frequency of IDTs—and the overall signal speed—has proven difficult. Most current SAW devices top out at a frequency of about 3 gigahertz, Zhang said, but in principle it is possible to make devices that are 10 times faster. Higher frequencies, however, demand more power to overcome the signal loss, and in turn, some features of the IDTs need to be increasingly small. While a 30 GHz device could transmit a signal more quickly, its operational range becomes limited.


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



To ensure that the transducers had the proper feature size, Zhang's team needed a material with a high acoustic velocity, such as diamond. They then coupled diamond, a material that changes its shape very little with electric voltage, with aluminum nitride, a piezoelectric material, and embedded the IDT inside their new SAW device.


The resulting device operated at a frequency of 17.7 GHz and improved power output by 10 percent compared to conventional devices using SAWs.


Zhang said she hopes this research will lead to SAW devices used in monolithic microwave integrated circuits (MMICs), low-cost, high-bandwidth integrated circuits that are seeing use in a variety of forms of high speed communications, such as cell phones.


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See You in 2018!

——誉芯金刚石

   Yuxin Diamond


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