基于MEMS的高Q值核磁共振平面微线圈

High-Q NMR Planar Microcoil Based on MEMS

为了提高核磁共振波谱检测信号的信噪比,实现对纳升级样品的检测,以及与微流控芯片集成,介绍了一种高品质因数(Q值)平面微线圈及其制作工艺。基于对信噪比的仿真计算,利用SU-8厚胶掩模光刻与直流铜电镀工艺,在玻璃衬底上得到几种几何参数优化的圆形与方形线圈。自行设计了一种直流铜电镀工艺,铜层生长速度约1.2μm/min。平面微线圈几何参数如下:内半径200μm^1 000μm,线宽/线间距20μm^80μm,圈数1~9圈,线圈厚度约12μm。利用Agilent 4294阻抗分析仪,测得85 MHz/2 Tesla下内半径1 000μm线圈的射频参数如下:RAC=7.25Ω,L=285 nH,Q=21。测得的Q值-频率曲线与仿真设计一致,即80 MHz附近Q值达到最大。与国内外其他测量结果相比,所得线圈品质因数较高。相对于双层铜电镀方案,本制作工艺操作简单,经一次电镀线圈即可成形,微米量级下更容易采用MEMS工艺制作平面线圈。另外,平面微线圈的开发可以将核磁共振(NMR)检测技术集成到微全分析系统中。

For increasing the Signal-to-Noise Ratio of Nuclear Magnetic Resonance experiment, detection for samples with nano-liter quantity and integration with microfluidic, the fabrication of planar microcoils with high Q value is presented. Based on the results of calculation for the simulation of SNR, several kinds of geometries of circular or square microcoils were fabricated on glass substrates using photolithography with SU-8 and DC copper electroplating. With the home-developed electroplating technology, the growing speed of copper layer is 1.2 μm/min approximately. The geometries for the microcoils fabricated successfully are inner radius 200 μm 1 000 μm, width ＆ separation 20 μm- 80 μm, number of turns 1 - 9, wire thickness 12μm. Using Agilent 4294 Impedance Analyzer, the measured RF parameters for No. 1000_1 Microeoil under 85 MHz/2 Tesla is RAC = 7.25 Ω, L = 285 nil, Q = 21. The trend of Q- frequency curve measured is compliance with that of the results of simulation, i. e. the Q value reaches maximum at 85 MHz. Compared with the measurements in other public literatures, the performances given in this paper are competitive. Unlike the double-layer electroplating scheme, this process of fabrication is simple and only one step of electroplating is needed. As a result the parasitic capacitance of shorted leaders of microcoil is decreased remarkable while increasing Q value. More important, compared with solenoid,in micron level the fabrication of planar microcoil is more compatible with MEMS. This work is an important step towards the integration of NMR detection into micro-total analysis systems （μTAS）.