Ecole Polytechnique Federale de Lausanne (EPFL), Laboratory of Life Sciences Electronics (CLSE), EPFL STI IBI CLSE Station 17, Lausanne, Switzerland.
Lab Chip. 2012 Nov 21;12(22):4920-8. doi: 10.1039/c2lc40582b.
This paper presents an experimental study on different microelectrode fabrication techniques, with particular focus on the robustness of the surface insulation towards typical working conditions required in lab-on-a-chip applications. Pt microelectrodes with diameters of 50 μm, 100 μm and 200 μm are patterned on a Si substrate with SiO(2) film. Sputtered SiO(2), low-pressure chemical vapor deposition (LPCVD) low-temperature oxide (LTO), Parylene C, SU-8, and dry-film were deposited and patterned on top of the chips as the passivation layer. This paper provides the detailed fabrication processes, the adhesion enhancement strategies, and the major advantages and disadvantages of each fabrication technique. Firstly, the quality and adhesion strength of the passivations were investigated by means of hydrolysis tests, in which sputtered SiO(2) and dry-film resist showed serious delamination issues and LTO showed minor defects. Secondly, the reliability of the microelectrodes was tested by impedance measurements after overnight ethanol incubation and self-assembled monolayer (SAM) formation. Thirty chips, representing a total of 300 electrodes, were measured, and statistical analyses of the results were conducted for each passivation technique. All of the electrodes passivated with these five techniques showed consistent impedance values after ethanol incubation. On the other hand, only LTO, Parylene C, and SU-8 ensured uniform electrical behavior after SAM formation. Having used both hydrolysis and impedance tests to verify the superior quality of the Parylene-based passivation, electrochemical experiments were performed to study the long-term stability of the passivation layer. Finally, the electrodes were incubated with electroactive alkanethiols functionalized with ferrocene. Square-wave voltammetry measurements demonstrated reproducible results on electrochemical label detection, which confirms the suitability of the Parylene passivation for charge-transfer-based measurements.
本文进行了不同微电极制造技术的实验研究，特别关注表面绝缘在微流控芯片应用中典型工作条件下的稳定性。在具有 SiO2 薄膜的 Si 衬底上用 Pt 制造出直径为 50μm、100μm 和 200μm 的微电极。溅射 SiO2、低压化学气相沉积（LPCVD）低温氧化物（LTO）、聚对二甲苯 C、SU-8 和干膜被沉积并图案化在芯片顶部作为钝化层。本文提供了详细的制造工艺、附着力增强策略，以及每种制造技术的主要优点和缺点。首先，通过水解试验研究了钝化层的质量和附着力强度，其中溅射 SiO2 和干膜抗蚀剂出现严重的分层问题，而 LTO 则显示出较小的缺陷。其次，通过过夜乙醇孵育和自组装单分子层（SAM）形成后的阻抗测量测试了微电极的可靠性。测试了 30 个芯片，总共 300 个电极，并对每种钝化技术的结果进行了统计分析。所有用这 5 种技术钝化的电极在乙醇孵育后都表现出一致的阻抗值。另一方面，只有 LTO、聚对二甲苯 C 和 SU-8 能确保在 SAM 形成后具有均匀的电性能。通过水解和阻抗测试验证了聚对二甲苯基钝化的卓越质量，随后进行了电化学实验以研究钝化层的长期稳定性。最后，将电极用功能化有二茂铁的电活性烷硫醇孵育。方波伏安法测量证明了电化学标记检测的重现性结果，这证实了聚对二甲苯钝化对于电荷转移测量的适用性。
