کنترل کیفیت فوق العاده میکروالکترود آرایه با استفاده از ولتامتری چرخه ای، طیف سنجی امپدانس الکتروشیمیایی و اسکن میکروسکوپ الکتروشیمیایی

Miniaturised amperometric transducers have been realised on silicon wafers integrating a disk ultra-microelectrode array (UMA) as working electrode, a large counter electrode and a Ag/AgCl pseudo-reference electrode in a three-electrode configuration. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) have been evaluated as tools for rapid on-wafer determination of characteristic device parameters. Here, we report on the application of an automated wafer prober in combination with appropriate electroanalytical techniques to realise an automated quality control of UMA on wafer level.

There is an increasing need for miniaturised sensors and systems in biochemical and biomedical analysis. This is mainly due to the specific properties of ultra-microelectrodes or ultra-microelectrode arrays (UMA) integrated in microanalysis systems such as high current density, inertness against stirring effects, and advanced signal-to-noise ratio [1], [2] and [3]. Microelectronic fabrication techniques have been used to manufacture related transducers on silicon wafer making use of the well developed production lines and lithographic techniques used for the production of electronic circuits [4], [5] and [6]. Here, the term ‘ultra-microelectrode’ is used for electrodes with diameters up to 20 μm, due to the fact that the term ‘microelectrode’ is frequently used for electrodes with significantly bigger dimensions [3]. A special type of transducer that has gained interest in recent years is the UMA for amperometric measurements, especially integrated within an on-chip three-electrode configuration [7]. However, although mass production techniques developed by the semiconductor industry are used for the fabrication of UMA prices are still high. This is at least partly due to the fact that up to now the quality of such UMA cannot be easily evaluated. Thus, the main costs turn up with the time consuming assembling and test of the devices and often much effort is put into a bad die. This had been very similar with microelectronic devices previously, and hence the semiconductor industry has developed sophisticated test equipment (e.g. wafer prober) for automated die tests on wafer level. It can thus be assured that each die is tested at maximum speed. Obviously, any attempt aiming on automated quality control systems has to be focused on wafer level in order to select those devices which meet the predefined quality at the earliest stage. Although the test equipment is commercially available, appropriate test methods for an automated test of each individual UMA on wafer level have to be developed.

Although N and Ru should be constant and determined by the UMA design, it has been demonstrated that the comparison of CV, EIS and SECM offers the opportunity to collect information concerning the number of electroactive ultra-microelectrodes within an array, which may differ significantly from the specified values due to passivation layer residues and poor ohmic resistances. The Ru is affected by poor ohmic resistances as can be derived by EIS. Based on the speed of the measurements, a combination of CV and EIS seems to be best suited to obtain information on N, Eeq and Ru, fully describing a UMA in a three electrode configuration. From our measurements, the time needed for the extraction of these parameters can be estimated to be about 10–15 s in the case of CV and EIS. Thus, automated quality control of UMA using these techniques may be possible.