Abstract
In this work, a low temperature (< 85∘C) packaging approach is proposed to implement highly stable ion-sensitive organic field-effect transistors (ISOFET) for multiple ion detection. It is realized by flip-chip bonding organic field effect transistor (OFET) transducers and sensitive/reference electrodes (SE/RE) on a plastic carrier using silver paste as the conductive adhesive and subsequent sealing with silicone sealant. A hollow structure is adopted to prevent OFETs from damaging by residual solvents in the adhesive and also from the influence of moisture in the air. The packaged OFET maintains high stability during the packaging process and presents good shelf-life performance with excellent bias stressing stability even after 24 days. A flexible tag consisting of three ISOFETs is demonstrated to properly detect Na+, K+, and H+ ions.
Highlights
Ion-sensitive field-effect transistor (ISFET) has received wide attention in the field of bio- or chemical sensing applications due to its ability to amplify the signal in-situ and implement sensor arrays for multiple ion detection [1,2,3]
The printed silver electrodes on one polyethylene naphthalate (PEN) plastic connected to those printed on another PEN substrate via silver paste between the bonding pads, which had a diameter of 1 mm
It is suspected that the polar solvents from conductive adhesive may adsorb onto the device during the packaging process and affect its performance
Summary
Ion-sensitive field-effect transistor (ISFET) has received wide attention in the field of bio- or chemical sensing applications due to its ability to amplify the signal in-situ and implement sensor arrays for multiple ion detection [1,2,3]. Compared to the traditional sensor using semiconductor polymer channel as ion-sensitive layer, the extended-gate type OFET sensor would provide more flexibility of utilization of organic semiconductors to enable the development of diverse ISOFET sensors. This architecture increases the flexibility of shape of the extended gates and their sensing functionalities, but it may induce external noise. A facial low-temperature packing approach was proposed for the assembly of flexible low-voltage ISOFETs without sacrificing device performance This was achieved by flip-chip bonding all the OFET transducers, sensing electrodes, and reference electrode on plastic carrier using silver paste as the conductive adhesive, and by sealing the elements with silicone sealant. Based on the developed approach, an integrated ISOFET tag consisting of three sensing channels was demonstrated to properly detect Na+, K+, and H+ simultaneously in solutions
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