芯片级原子器件MEMS碱金属蒸气腔室制作

Microfabrication of MEMS alkali metal vapor cells for chip-scale atomic devices

提出了基于两步低温阳极键合工艺的碱金属蒸气腔室制作方法,用于实现原子钟、原子磁力计及原子陀螺仪等器件的芯片级集成。由微机电系统(MEMS)体硅工艺制备了腔室结构。首先采用标准工艺将刻蚀有腔室的硅圆片与Py-rex玻璃阳极键合成预成型腔室,然后引入氮缓冲气体和由惰性石蜡包覆的微量碱金属铷或铯。通过两步阳极键合来密封腔室,键合温度低于石蜡燃点198℃。第一步键合预封装腔室,键合电压小于缓冲气体的击穿电压。第二步键合在大气氛围中进行,电压增至1 200V来增强封装质量。通过高功率激光器局部加热释放碱金属,同时在腔壁上形成均匀的石蜡镀层以延长极化原子寿命。本文实现了160℃的低温阳极键合封装,键合率达到95%以上。封装的碱金属铷释放后仍具有金属光泽,实现的最小双腔室体积为6.5mm×4.5mm×2mm。铷的吸收光谱表明铷有效地封装在腔室中,证明两步低温阳极键合工艺制作碱金属蒸气腔室是可行的。

This paper reported on the mierofabrication of alkali metal vapor cells based on the two-step low temperature anodic bonding for the chip-scale integration of atomic clock, atomic magnetometer, atomic gyroscope and other atomic devices. Cell structures were fabricated by Micro-electromecbanical System （MEMS） bulk silicon process, and the etched silicon with cells was firstly bonded to Pyrex glass to fabricate preformed chambers hy the standard anodic bonding process. Then, nitrogen buffer gas and micro-scale alkali metal （rubidium or cesium） were introduced into the preformed cells. The two-step anodic bonding process was used to seal the cells at a temperature lower than the paraffin flash point （198 ℃）. In the first step, bonding voltage was lower than the breakdown voltage of ni- trogen buffer gas to pre-seal the cells. In the second step, the bonding was in air atmosphere, and the bonding voltage increased up to 1 200 V to strengthen packaging quality. A high power laser system locally heated the micro-scale alkali metal packets to release alkali metal, and a uniform coating of paraffin was formed on cell walls to prolong the life of the polarized atoms. With proposed method, 95~ bonding is achieved by the two-step low temperature anodic bonding, and the alkali rubidium still has a metallic luster after anodic packaging. The achieved minimum volume of double-cells is about 6.5 mm× 4.5 mm× 2mm. Rubidium absorption spectrum shows that alkali rubidium is effectively encap- sulated in the cells. It is feasible to fabricate MEMS alkali metal vapor cells by the two-step low tem- perature anodic bonding process.