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流体晶体管引导液体电脑时代
诸平
据物理学家组织网（Phys.org）2017年11月3日转载来自美国卡内基梅隆大学工程学院（Carnegie Mellon University Mechanical Engineering）的消息，该大学的研究人员利用室温下的铟镓合金，可用于创建可伸缩的电路布线和电气开关。晶体管是进行信号和数据处理的微小电开关,它也是每个电子设备背后的脑动力，从笔记本电脑、智能手机到数码恒温器无不涉及到晶体管。而且随着电脑变得越来越小，功能却要求越来越高大，晶体管的体积也在不断继续缩小。然而,当我们希望建立湿软的,人性化的机器，并使其有柔软的自然生物体的外观和感觉时,我们需要超越用于创建电气开关和电路的刚性材料的视野。
卡内基梅隆大学柔软机器实验室（Soft Machines Lab at Carnegie Mellon University）的机械工程师卡梅尔·马吉迪（Carmel Majidi）和詹姆斯·威斯曼（James Wissman），一直在关注创建电子学的新方法,即不仅仅是数字化功能的，而且还要柔软和可变形的。而不是从刚性金属如铜或银来制作电路,他们使用的是一种特殊的、在室温下是液态的金属合金。这种合金是由铟和镓混合的，是一种可以替代汞的室温下以液态存在的无毒合金材料，可以注入橡胶制作出类似自然皮肤一样柔软和富有弹性的电路。
与北卡州立大学（North Carolina State University）的迈克尔·迪基(Michael Dickey)合作,他们最近发现这种液态金属电子产品，不仅可以用于柔性电路连接,也可以用来制作电气开关。这些流体晶体管通过打开和关闭两个液态金属液滴之间的联系而进行工作。当在一个方向上应用电压降时,液滴移向彼此,合并成一金属桥来传导电流。当在不同方向施加电压时,液滴自发地分开将开关打开。通过在开与关之间的快速交替,打开开关状态仅仅需要很小的电压即可,研究人员利用液滴能够模仿传统的晶体管特性。
研究团队利用毛细管的不稳定性得到这种结果。卡梅尔·马吉迪说：“我们一直看到毛细管的不稳定性,如果你打开水龙头，实际上流量很低,有时候你会看到从稳定流到单独液滴的转变。这是被称为瑞利不稳定性（Rayleigh instability）。”
研究人员必须找到一种方法来诱导这液态金属的这种不稳定性,这样它可以无缝地从一个液滴过渡到两个液滴。在氢氧化钠浴内履行了一系列液滴测试后,他们意识到这种不稳定性是由一个施加电压和一个电化学反应之间的耦合而驱动的。这种耦合引起了液滴表面氧化梯度,从而导致液滴的表面张力梯度,最终驱使两液滴分离。更多信息请注意浏览原文或者相关报道。
Transistors, those tiny electrical switches that process signals and data, are the brain power behind every electronic device – from laptops and smartphones to your digital thermostat. As they continue to shrink in size, computers have become smaller, more powerful, and more pervasive. However, as we look to build squishy, human-friendly machines that have the look and feel of soft natural organisms, we need to look beyond the rigid materials used to create electrical switches and circuits.
Mechanical engineers Carmel Majidi and James Wissman of the Soft Machines Lab at Carnegie Mellon University have been looking at new ways to create electronics that are not just digitally functional but also soft and deformable. Rather than making circuits from rigid metals like copper or silver, they use a special metal alloy that is liquid at room temperature. This alloy, made by mixing indium and gallium, is a non-toxic alternative to mercury and can be infused in rubber to make circuits that are as soft and elastic as natural skin.
Teaming up with Michael Dickey at North Carolina State University, they recently discovered that liquid metal electronics are not only useful for stretchable circuit wiring but can also be used to make electrical switches. These fluidic transistors work by opening and closing the connection between two liquid metal droplets. When a voltage drop is applied in one direction, the droplets move towards each other and coalesce to form a metallic bridge for conducting electricity. When voltage is applied in a different direction, the droplets spontaneously break apart and turn the switch to open. By quickly alternating between an open and closed and open switch state with only a small amount of voltage, the researchers were able to mimic the properties of a conventional transistor.
The team came to this result by exploiting a capillary instability. "We see capillary instabilities all the time," says Majidi. "If you turn on a faucet and the flow rate is really low, sometimes you'll see this transition from a steady stream to individual droplets. That's called a Rayleigh instability."
The researchers had to find a way to induce this instability in the liquid metal such that it could seamlessly transition from one droplet to two. After performing a series of tests on droplets within a sodium hydroxide bath, they realized that the instability was driven by the coupling between an applied voltage and an electro-chemical reaction. This coupling caused a gradient in the droplet's surface oxidation, which then resulted in a gradient in the droplet's surface tension, which finally drove the separation of the two droplets.
The team calls it a liquid metal transistor because it has the same kind of circuit properties found in a conventional circuit transistor. "We have these two droplets that are analogous to source and drain electrodes in a field-effect transistor, and we can use this shape programmable effect to open and close the circuit," says Majidi. "You could eventually use this effect to create these physically reconfigurable circuits."
The applications for this type of programmable matter are endless. If materials can be programmed to change shape, they can potentially change their function depending on their configuration, or even reconfigure themselves to bypass damage in extreme environments. "It could be on a structure that's undergoing some very large physical deformations, like a flying robot that mimics the properties of a bird," says Majidi. "When it spreads its wings, you want the circuitry on the wings to also deform and reconfigure so that they remain operational or support some new kind of electrical functionality."
Other applications could include liquid computers for uses in technologies of the future. Think of miniature computers that interface with biological material to monitor disease in the body or restore brain function to a stroke survivor. Imagine search and rescue robots that can self-assemble new parts when damaged. Although it sounds like science fiction, liquid computing might one day be as commonplace as today's laptops.
Wissman, Dickey, and Majidi summarized their research in a paper published in the journal Advanced Science.
Liquid metal brings soft robotics a step closer
"Field-controlled electrical switch with liquid metal," Advanced Science, DOI: 10.1002/advs.201700169 , http://onlinelibrary.wiley.com/doi/10.1002/advs.201700169/full
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