美国伦斯勒理工学院开发新式液体镜头有可能帮助改进浸没式光刻设备

美国伦斯勒理工学院最近开发出一种新式液体镜头，能通过超小型的微流体活塞、以电气方式调整焦距，不须外加零件。此前，液体镜头已经被应用在浸没式光刻设备，用以提升光刻分辨率，使得目前的CMOS工艺得以继续向90纳米以下的工艺线宽拓展。但必须以人工对焦的方法来消除这种镜头中不受控制的空气液滴。

伦斯勒理工学院表示，他们所开发的电磁式液体镜头适合各种精密影像应用，包括浸没式光刻设备、人工视网膜以及手机用的超低功耗摄影机。这项技术是该校教授Amir Hirsa的研究成果，他的工作起始于一项看似漫不经心的游戏。Amir Hirsa 以磁场小心翼翼地震荡饱含铁纳米粒子的流体液滴，液滴内部的流体就会像帮浦活塞一样被上下抽吸，并因此能进行液体镜头的对焦。Amir Hirsa发现这样做所需的功耗甚至低于采用微机电系统组件(MEMS)的方案。

Microfluidic pumps focus liquid lens

R. Colin Johnson

Liquid lenses are already used in immersion lithography to boost resolution, but the free-air droplets must be manually adjusted for proper focus. Now Rensselaer Polytechnic Institute (RPI) has shown a liquid lens with a focal length that can be electrically adjusted with tiny microfluidic pistons with no moving parts. RPI claims its electromagnetic liquid lens could boost all types of precision imaging applications, from immersion lithography to implantable retinas to the ultra-low power cameras on cell phones.

RPI's technique, developed by professor Amir Hirsa, uses fluids saturated with iron nanoparticles. By carefully oscillating a ferro-fluidic droplet with a magnetic field, the fluids inside can be pumped up-and-down like a piston, allowing the focal length of a lens to be adjusted using even less energy than a micro-electro-mechanical system (MEMS). Because the fields are generated use alternating currents, the lens is constantly cycling between its closest and furthest focal lengths, but the researchers say that software algorithms can easily eliminate any out-of-focus frames. In its demonstrations, the researchers were able to capture in-focus 30 frame-per-second videos as a proof of concept.

The demonstration set-up housed an opaque ferro-fluidic droplet—the piston—in one hole drilled next to another holding the transparent lens droplet in a solid substrate separating two sealed chambers filled with water (see figure). Electromagnetic pulses then forced the piston droplet to vibrate up and and down in its hole. Magnetic, capillary and inertial forces combined to cause the second droplet—the lens—to follow the movement of the piston droplet, setting it to oscillating between its maximum and minimum focal lengths.

Hirsa's collaborators on the project included MIT Lincolm Lab researcher Bernard Malouin, Michael Vogel, a private research consultant, RPI doctoral candidate Joseph Olles, and former postdoctoral researcher Lili Cheng, now at General Electric Global Research. Funding was provided by the Defense Advanced Research Projects Agency (DARPA).

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