Research On The Fabrication Of Flexible Dry Electrode For ECG Monitoring

Electrocardiogram(ECG)is of critical importance for health monitoring and medical diagnosis.Currently,the electrocardiographic electrode most commonly used for ECG monitoring is an Ag/AgCl electrode with a conductive gel,also known as wet electrode.The conductive gel over the electrode can help establish a reliable electrode-to-skin connection and decrease the contact impedance.However,the gel also brings about two issues.On the one hand,the gel will dehydrate over time,and in turn the quality of the measured signal will gradually degrade.On the other hand,the conductive gel may cause dermal irritation and even allergies for long-term use.In this paper,two flexible dry electrodes without conductive gel were designed and fabricated.First,a flexible dry electrode based on polyimide substrate was designed.The electrode consists of two layers of gold and polyimide.A flexible polyimide film is selected as a substrate to ensure that the electrode can be freely bent.At the same time,the gold electrode is designed as an island bridge structure to initially increase stretchablity.The patterning of the gold layer is achieved by a photolithography process.Its ECG recording performance is comparable to commercial wet electrode.Moreover,the flexible dry electrode can be used repeatedly and has no significant change in recording performance.Next,a three-layer structure of the stretchabile dry electrode was designed.The electrode is composed of a polyurethane-polyimide-gold three-layer structure.A stretchabile polyurethane film is selected as a substrate,and a polyimide material is used as an intermediate layer,which is placed between the gold electrode and the polyurethane film.The electrode has good stretchability and conformality.In order to fabricate a three-layer structure of stretchabile dry electrodes,a sacrificial-layer assisted one-step transfer printing method is proposed.An Au electrode layer was sputtered on a silicon wafer with a Cu sacrificial layer,a PI film was spin-coated on the Au layer and patterned by a simple standard photolithography process,the Au layer was patterned by wet etching using the patterned PI film as the etching mask,and the patterned Au layer and PI film were transferred to a stretchable film in one step by etching away the Cu sacrificial layer.A tape-based three-layer dry electrode was fabricated.This transfer printing method not only involves a time-consuming RIE process,but also requires conducting the tricky transfer process for two times.That simplify the operation process and improve the process efficiency.Finally,the performance of the stretchable dry electrode was tested.In terms of mechanical properties,the stretchable dry electrode can withstand 10% tensile strain;in terms of skin-electrode impedance,the contact resistance of the stretchable dry electrode is better than that of the hard dry electrode;in terms of ECG monitoring,the dry electrode can be extended The similarity of the existing commercial wet electrode ECG signals is as high as 96%;in the long-term use,after 10 min,2 h,24 h and 48 h monitoring,the signal-to-noise ratio(SNR)of the ECG signals obtained by the electrode test The fluctuation is small;in the aspect of motion monitoring,ECG characteristics of the stretchable dry electrode monitoring are clearly visible when the tester runs at 5 km/h.It proves that the three-layer structure of the stretchable dry electrode designed in this paper can dynamically monitor the human body electrocardiogram for long-term use in cardiovascular disease detection and medical diagnosis.