Thermally Controlled, Patterned Graphene Transfer Printing for Transparent and Wearable Electronic/Optoelectronic System

Abstract

Graphene has been highlighted as a platform material in transparent electronics and optoelectronics, including flexible and stretchable ones, due to its unique properties such as optical transparency, mechanical softness, ultrathin thickness, and high carrier mobility. Despite huge research efforts for graphene‐based electronic/optoelectronic devices, there are remaining challenges in terms of their seamless integration, such as the high‐quality contact formation, precise alignment of micrometer‐scale patterns, and control of interfacial‐adhesion/local‐resistance. Here, a thermally controlled transfer printing technique that allows multiple patterned‐graphene transfers at desired locations is presented. Using the thermal‐expansion mismatch between the viscoelastic sacrificial layer and the elastic stamp, a “heating and cooling” process precisely positions patterned graphene layers on various substrates, including graphene prepatterns, hydrophilic surfaces, and superhydrophobic surfaces, with high transfer yields. A detailed theoretical analysis of underlying physics/mechanics of this approach is also described. The proposed transfer printing successfully integrates graphene‐based stretchable sensors, actuators, light‐emitting diodes, and other electronics in one platform, paving the way toward transparent and wearable multifunctional electronic systems.

Nanomaterial‐Enabled Wearable Sensors for Healthcare

“…The smartband was fabricated by transfer printing of graphene. [37] In another work, a wearable diabetes patch demonstrated the feasibility of close-loop wearable monitoring and therapeutic treatments. [170] As illustrated in Figure 8d, a sweat control layer was used to collect the sweat for sensing, multiple sensors (humidity, PH, glucose, and strain gauge) were used to measure the glucose level and tremor signals, a thermally triggered drug-loaded microneedle in conjunction with a temperature sensor and a heater were used to perform transcutaneous drug delivery.…”

“…Reproduced with permission. [37] d) Schematic of the wearable diabetes patch with sweat collecting, electrochemical sensing and transcutaneous drug delivery enabled by a thermal responsive microneedle array. Reproduced with permission.…”

“…For instance, actuators or stimulators may be incorporated to achieve interactive devices that can interact with human body, another device or the environment. [22,37,170,187] Drug-delivery platforms can be integrated to enable therapeutic treatments in response to the information collected by the wearable sensors. [188][189][190] Energy scavengers could negate the need for frequently charging batteries or completely replace the batteries.…”

“…In an advanced wearable system with both sensing and therapeutic treatment capabilities, [37,79,170] highly sensitive multimodal sensors can monitor the physiological parameters to evaluate health conditions or monitor body motions to access the effectiveness of rehabilitation. The real-time data can be sent wirelessly to the wearer, a caregiver, or an emergency center.…”

“…[18,[33][34][35] To fabricate the wearable sensors, conventional lithographic processes can be extended to pattern nanomaterials. [23,[36][37][38] Solution based processing methods such as spray coating, [25,39,40] drop casting, [41][42][43][44][45] spin coating, [46,47] dip coating, [48] vacuum filtration, [49][50][51] and layer-by-layer assembly [52] were commonly used for fabrication of nanomaterial-based sensors. Direct spinning of CNTs onto a substrate or into yarns [53][54][55] and electrospinning of nanofibers or NWs were reported to produce fiber-like nanomaterials.…”