摘要
~5um厚的電路製作過程：使用臺式激光打印機將圖案打印在臨時的紋身紙上，接下來使用銀墨水和共晶鎵−銦(EGaIn)液態金屬合金塗覆。【The ∼5 μm thick circuit is fabricated by printing the pattern over a temporary tattoo paper using a desktop laser printer, which is then coated with a silver ink and eutectic gallium−indium (EGaIn) liquid metal alloy】
形成的“Ag-In-Ga”路徑高導電，並且當適應3D表面是維持着低的導電電阻【The resulting “Ag−In−Ga” traces are highly conductive and maintain low electrical resistivity as the circuit is stretched to conform to nondevelopable 3D surfaces】
通過引入一種新興的z-axis的導電接口，該結構有磁性排列的EGaIn塗覆的嵌入在PVA(polyvinyl alcohol)中的Ag-In微粒組成，也提出了表面貼裝微電子芯片的集成化【We also address integration of surface-mounted microelectronic chips by introducing a novel zaxis conductive interface composed of magnetically aligned EGaIn-coated Ag−Ni microparticles embedded in polyvinyl alcohol (PVA)】
這種“zPVA導電膠”能與管腳尺寸爲300um的微芯片形成穩定的點接觸【This “zPVA conductive glue” allows for robust electrical contacts with microchips that have pins with dimensions as small as 300 μm】
如果打印在臨時的紋身轉移紙上，可以通過hydrographic transfer將電路轉移到3D表面上【If printed on the temporary tattoo transfer paper, the populated circuit can be attached to a 3D surface using hydrographic transfer】
打印和接口處理都可以在室溫下進行【Both printing and interfacing processes can be performed at the room temperature】
我們演示了一些例子，包括人體表皮上用於肌電圖信號採集的電子紋身，帶有觸控按鈕的交互式電路，轉移到機器假肢上3D打印外殼上的LED和轉移到到3D表面上的接近度測量皮膚【We demonstrate examples of applications, including an electronic tattoo over the human epidermis for electromyography signal acquisition, an interactive circuit with touch buttons, and light-emitting diodes transferred over the 3D printed shell of a robotic prosthetic hand, and a proximity measurement skin transferred over a 3D surface】
introduction
Electronics circuits that interface with the human body or surface of objects can enable functionalities such as acquisition of biosignals, detection of human touch, proximity, temperature, and energy harvesting.[1,2] These circuits can also integrate antennas and display[3] over the surface of the object, and turn them into an interactive reciprocal surface, which has applications in human−machine interfaces (HMIs) and large area displays. Moreover, when integrated over the human epidermis, these circuits enable applications in wearable computing and health monitoring 與人臉表皮集成後，這些電路可用於可計算穿戴和健康監測
[4,5]最近致力於發展新的製造技術來建立集成的，三維材料系統來實現這些功能。【Recent efforts have focused on additive manufacturing techniques to create integrated, three-dimensional (3D) material systems that achieve these functionalities】
這些3D打印技術已經涵蓋廣泛的材料：
- carbon nanotubes for super capacitors[6]
- ferromagnetic photopolymers for magnetic sensors[7]
- shape memory polymers for “4D printing”[8]
- conductive materials for strain or pressure sensors[9,10]
最近有一些在3D表面[11]或人體[12]打印電子器件和其他功能材料 的示例【There have also been recent demonstrations of printing electronics and other functional materials over an existing 3D surface[11] or on the human body [12] 】
這邊說了一下3D打印的缺點，能準確的隨着表面形態沉積導電油墨或漿。通常很慢並且沒有統一的方法。【Although promising, direct printing over three dimensional surfaces is a complex process, requiring the print head to precisely follow the surface morphology to deposit a conductive ink or paste. This is generally a slow and not a scalable process】
一種可能替代的方法是，打印2D電路，能轉移到3D表面上。
這能通過hydroprinting實現，當物體從水缸中移開時，浮在水缸表面的有圖案的薄膜被轉移到三維物體的表面。【One possible alternative is 2D printing of circuits which can be transferred to a 3D surface。 This can be accomplished through hydroprinting, in which patterned thin films floating on the surface of a water bath are transferred to the surface of 3D objects as the objects are removed from the bath】
但是，將這種技術推廣到印刷電子產品可能具有挑戰性，因爲成功地將2D電路轉移到複雜的，可擴展的3D表面要求電路可彎曲和可伸縮。【However, extension of this technique to printed electronics can be challenging because successful transfer of a 2D circuit over a complex, nondevelopable 3D surface requires the circuit not only to bend but also to stretch】
爲了克服這一困難，工程師們已經開發出由傳感器和數字集成電路芯片組成的“表皮電子產品”，這些產品被集成到一種超薄的載體薄膜中，能夠輕易地轉移到人體皮膚上[13]【To accomplish this, engineers have developed “epidermal electronics” composed of sensors
and digital integrated circuit chips incorporated into an ultrathin carrier film that can readily transfer to the human skin】
他們就像電子文身一樣工作，已經用於：
- biomonitoring [13]
- implantable energy harvesting[14]
- pulse oximetry[3]
- neural interfaces[15]
製造軟性物質電子器件開創性的努力主要集中在確定性的電路結構，其中可延伸性主要是利用具有波形或蛇形幾何結構的電路佈線[13]。【Seminal efforts on fabrication of soft-matter electronics have focused on deterministic circuit architectures in which stretchable functionality is achieved with circuit traces that have a wavy or serpentine geometry】
儘管很有潛力，但是這些方法都要依賴於潔淨室光刻或特殊處理過程，因而很難低成本打印或快速原型設計。【However, although promising, these approaches typically rely on cleanroom lithography or specialized processing steps that are difficult to perform with low-cost printing or rapid prototyping methods】
將表皮電子擴展到機器人，HMIs的應用需要繼續研究新的材料結構和處理技術，以至於能更廣泛的使用。【Extending epidermal electronics to applications in robotics, HMIs require continued exploration of new material architectures and processing techniques that are accessible to a wider user community】
特別的，這些方法應當不依賴於淨室製造方法（比如光刻）和高溫處理過程。另外，這些電路應當當能夠直接與微電子芯片或PCBs連接進行數據處理和傳輸，而不需要額外的電線連接。【In particular, these approaches should have limited dependency on clean-room fabrication methods (e.g., photolithography) or high-temperature processing steps. Moreover, such circuits should be able to directly interface with microelectronic chips or printed circuit boards (PCBs) for data processing and transmission without the need for external electrical wiring.】
我們利用桌面印刷和水印轉移技術展示了一種新的方法，來快速製造類似於紋身的薄膜電路【Here, we demonstrate a novel method for rapid fabrication of tattoo-like, thin-film circuits with integrated microelectronics that utilizes desktop printing and hydrographic transfer techniques.】
通過取消了對微製作，後燒結， 薄膜金屬沉積，和平板印刷圖案，目前的工作大大簡化了步驟。【The current work greatly simplifies these manufacturing techniques by eliminating the need for microfabrication, post sintering, thin-film metal deposition, and lithographic patterning】
與其他製造超薄和表皮電子的方法不同，本方法使用和商用桌面打印機制作，不需要昂貴的處理步驟和自制器材。【Unlike other methods for producing ultrathin and epidermal electronics, fabrication can be performed using a commercially-available desktop printer
and eliminates the need for expensive processing steps or custom-built equipment.】
電路能打印到紋身轉移紙(tansfer tattoo paper TTP)或 水紋紙(hydrographic paper)，並轉移到身體或3D平面上(Figure 1A)【Circuits can be printed on a transfer tattoo paper (TTP) or hydrographic paper and transferred to the body or a 3D surface】
本任務中使用的TTP有一層超薄(<5um)的載體膜，一種水溶性聚乙烯醇(PVA)層和 背紙組成【The TTP used in this work is composed of an ultrathin (<5 μm) carrier film, a water soluble polyvinyl alcohol (PVA) layer, and backing paper (Figure S1)】
當與水接觸時，載體膜從紙上分離，漂 浮在水的表面，載體膜可以在水箱中轉移到不同的材料上比如皮膚，衣服，塑料，金屬和玻璃 (Figure 1A−D).【When in contact with water, the carrier film separates from the paper, and floats over the surface of the water, which can be then transferred in a water tank over various materials, for example, skin, cloth, plastic, metal, and glass】
電路是通過首先使用桌面打印機在TTP上打印電路模板來創建的。【Circuits are created by first printing a circuit template on TTP using a desktop printer.】
?有點不太明白過程呢！！！
電路可以使用噴墨打印機打印銀納米顆粒墨水實現，接着使用液相的共晶鎵−銦(EGaIn 75.5 wt % Ga, 24.5 wt % In, melting point: 15.7 °C)合金覆蓋打印線路[16]
EGaIn 的塗覆使得導電率提高了6個數量級，使得電路對於機械應變的容忍度提高【EGaIn coating increases the conductivity of the printed AgNPs by 6 orders of magnitude and makes the circuits considerably tolerant to mechanical strain】
我們提出了一種新的方法制造“Ag-In-Ga”電路，首先使用打印碳粉(print toner)打印不導電模板，接着用銀漿料(sliver paste)覆蓋,銀漿會選擇性地粘附在印刷的墨粉上,作爲潤溼層沉積EGaIn。【Here, we show a novel method to produce “Ag−In−Ga” circuits, which starts by using a desktop laserjet to print a nonconductive template with print toner and then coat the
template with silver paste. The silver paste will selectively adhere only to the printed toner ink and function as a wetting layer on which to deposit the EGaIn】
在兩種情況下，產生的電路高導電，在轉移後，能完美貼合不可展開的3D表面，而導電率不會降低【In both cases, the resulting circuits are highly conductive, and after the transfer, they conform to nondevelopable 3D surfaces without losing their conductivity】
與納米銀顆粒油墨相比，這種方法簡單快捷，無需對噴墨打印機進行修改、清洗、墨盒充墨，也無需由於堵塞而 對墨盒進行週期性的濾墨、聲濾、更換或清洗等操作。【When compared to AgNP inks, this method is simpler and faster because it eliminates the need for modification of an inkjet printer, cleaning, and filling the cartridges with the ink, as well as periodical ink filtering, ink sonication, and replacement or cleaning of the cartridge due to clogging.】
當然，導電漿料使用微顆粒和微片，通過改變填料含量、填料尺寸和載體材料等參數，它們在導電性和附着力方面更容易生產和定製。【Also, conductive pastes are made with microparticles or microflakes; they are considerably easier to produce and customize in terms of conductivity and adhesion, by changing parameters such as the filler content, the filler size, and the carrier material】
因而與AgNP相比，種類更廣泛，價格更實惠。【Therefore, they exist in a wider variety and are more affordable when compared to AgNP inks】
然而之前，他們的沉積需要模板和後烘乾步驟，這與噴墨打印相比是一個缺點。 所有的這些要求在我們的方法下都不需要了【However, previously their deposition had required stencils and a postbaking step, which is a disadvantage compared to inkjet printing. Both of these requirements have been eliminated with the current technique.】
儘管提出的方法促進了互連電路的打印，這些電路的實際應用仍然依賴於發展方法來與外部電路的更穩定電連接和與印刷圖案與微芯片直接接觸.在本文中，我們引入了新的Z-zhou的導電接口來解決這兩個問題(Figure 1D)【Although the presented method significantly facilitates printing of the circuit interconnects, actual application of these circuits still depends on development of methods for robust electrical interfacing with external circuits and direct interfacing of the printed pattern with microchips. In this article, we address both by introducing a novel z-axis conductive interface (Figure 1D)】
接口由嵌在PVA薄膜的垂直排列的磁顆粒組成。這種凝膠狀的“zPVA膠”可用於微電子器件和柔性電路與薄膜表面的連接。【The interface is composed of vertically aligned magnetic particles embedded in a PVA film. This gel-like “zPVA glue” can be used for interfacing the
thin-film skin with microelectronics and flex circuits】
zPVA的凝膠到固體轉化是通過溶液中水分的蒸發實現的，可以在室溫下進行【The gel to
solid transformation of zPVA is achieved by evaporation of water in the solution, which can be performed at room temperature】
與之前基於PDMS的各向異性的導電體相比[17,18]，zPVA可以貼合到更廣泛材料上，包括基於PVA的轉印紙。【Compared to previous PDMS-based anisotropic conductors,[17,18] zPVA adheres to a wider range of materials, including the PVA-based transfer paper.】
聚乙烯醇：可用於製作膠水https://zh.wikipedia.org/wiki/%E8%81%9A%E4%B9%99%E7%83%AF%E9%86%87
background
我們製造可拉伸的電子是建立在之前"雙極性"材料架構的基礎上的，該方法將EGaIn與金屬模板結合創造機械魯棒性高的電路。【Our approach to thin-film stretchable electronics builds on previous efforts in “biphasic” material architectures that combine EGaIn with metallic templates to create mechanically robust circuits】
在這些方法中，EGaIn塗覆在濺鍍沉積的金屬(Au, Ag, Au)薄膜上，使用光刻[19-21]或紫外激光微加工[22,23]來刻畫金屬薄膜圖案。【EGaIn is coated on a sputter-deposited thin film of the metal (Au, Ag, or Cu) that is patterned using either photolithography or UV laser micromachining】
其他的努力集中在能夠打印在可拉伸基底上的EGaIn納米顆粒的合成[24]和“機械燒結”來創造導電電路[25,26]。【Other research efforts focused on synthesis of EGaIn nanoparticles that can be printed on a stretchable substrate and “mechanically sintered” to create conductive traces】
我們改進了這種方法，通過使用任何標準的商用噴墨打印機將圖案打印在TTP薄膜上。【We improve upon this past work by introducing “facile” fabrication techniques that enable patterning on a TTP thin film using any standard commercial desktop printer】
EGaIn輔助的AgNP的室溫燒結的分析本文沒有涉及，已經在[16]中涉及。相反的，我們聚焦在能提供快速製造且不需要潔淨室或特殊處理儀器的技術上。【The analysis of the EGaIn-assisted room temperature “sintering” of the AgNP ink is not the focus of this article and was covered in a recent companion study.16 Instead, we focus on techniques that allow for rapid fabrication of thin-film circuits without dependency on a clean-room or specialized processing equipment.】
我們展示了一些人機交互的應用和如何快速打印並將這些薄膜電路轉移到3D表面上，並且使用它作爲感知皮膚。【As a case study, we demonstrate applications to human−machine interaction and demonstrate how one can be rapidly printed and transfer these thin-film circuits to 3D surfaces, and use it as a sensing skin】
特別的，我們展示了使用hydroprinting方法可以將電路轉移到不可擴展的3D表面上(比如，球形)和有銳利邊緣的表面。【In particular, we show that the circuits can be transferred over complex nondevelopable 3D surfaces (i.e. spherical features), and over sharp edges using hydroprinting methods.】
我們也展示了這種電路能自粘附於人體表皮，總肌肉活動中獲取生物電勢，比如肌電圖(EMG)。【We also demonstrate that such circuits can self-adhere to the human epidermis
for acquisition of biopotentials from muscle activity, for example, electromyography (EMG)】
儘管由PEDOT:PSS 聚合物【27】和打印銀油墨【28】的自由納米薄膜已經展示位可以在水中釋放的薄膜導體，本工作利用“Ag-In-Ga”互聯結構可伸縮和能轉移到更復雜表面，包括180度的摺疊的優勢，比前者更優勢。【Although free-standing nanofilms composed of the poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS) polymer and printed Ag ink have been previously shown as thin-film conductors that can be released in water, the current work improves over its predecessors by taking advantage of “Ag−In−Ga” interconnects which are stretchable and allows the transfer to be performed over more complex surfaces, including 180° folding.】
除此之外，使用zPVA各向異性導體密封電路能允許表面填充SMD組件和與外部電路形成魯棒性更高的電連接。【In addition, sealing the circuit with a zPVA anisotropic conductor allows the surface to be populated with SMD components and enables robust interfacing with external electronics】
最後，簡易的製造技術允許粘性銀膠料的無模板處理，能夠快速製作定製電路的原型，比如用於生物監測應用的多電極模式的保形的和不易察覺的紋身狀電路。【Finally, the facile fabrication technique presented here allows stencil-free disposition of viscous silver pastes that permits rapid prototyping of customized circuits, such as multielectrode patterns for conformal and imperceptible tattoo-like circuits for biomonitoring applications.】
results
製造過程分爲四個步驟：
- circuit printing
- materials postprocessing
- microchip integration
- hydrographic transfer
在第一階段，Figure 2A
使用臺式激光打印在TTP薄膜上打印圖案，然後通過銀膠料或環氧樹脂的選擇性沉積製造電路。爲了提高導電性和延伸性，電路結社覆蓋一層EGaIn，步驟如Figure 2A和Movie S1中展示，描述在materials and methods章節。【a circuit is produced through selective deposition of silver paste or epoxy on a TTP film after printing the pattern by a desktop laser printer (Figure 2A). In order to improve electrical conductivity and stretchability, the circuits are then coated with EGaIn using the steps presented in Figure 2A, Movie S1, and described in the Materials and Methods section】
液態金屬(LM)合金當暴露在弱(2 wt%)的冰醋酸水溶液或鹽酸蒸氣時會選擇性的潤溼Ag痕跡上(Figure 2A Movie S1)，這就是說，在初始沉積之後，EGaIn氧化物會浸潤TTP表面，包括打印和非打印區域，但是，使用
CH3COOH或 HCl處理過的EGaIn會移除表面氧化物(),這回導致未塗覆的TTP去浸潤(由於未氧化EGaIn的表面張力大)和對於銀顆粒有更強的粘附能力。氧化物的去除也可以使用氫氧化鈉溶液，其中，銀顆粒就像“錨點”一樣防止LM去浸潤，和沖洗掉。【The liquid metal (LM)
alloy selectively wets to Ag traces when exposed to a weak (2 wt %) acetic acid solution or hydrochloric acid vapor (Figure 2A, and Movie S1). That is, after the initial deposition, EGaIn oxide wets the TTP surface, including the printed and nonprinted areas. However, treating EGaIn with CH3COOH or HCl removes its surface oxide (Ga2O3), which results in dewetting from the uncoated TTP (because of the high surface tension of nonoxidized EGaIn) and stronger adhesion (and possible alloying) to the silver particles. Oxide reduction can also be performed with aqueous solutions of NaOH,29 in which case the silver particles act as “anchoring points” that prevent the LM from dewetting and rinsing away.】
得到的“Ag-In-Ga”電路使用zPVA複合物覆蓋密封(Figure 2B),有垂直排列的嵌在PVA膠中的導電顆粒組成(Figure 1D)。【The resulting “Ag−In−Ga” circuit is sealed with a coating of zPVA composite (Figure 2B), which is composed of vertically aligned conductive particles embedded in a PVA gel (Figure 1D)】
封口處只在垂直厚度方向上導電，使的在電路終端和表面組裝微電子和外部電路的引腳間形成電連接。【The seal is conductive only through its thickness and enables the formation of electrical vias between the terminals of the circuit and pins of surface-mounted microelectronics and circuit board connectors.】
使用鍍銀鎳顆粒與聚乙烯醇混合製備複合材料，使用thin-film applicator(ZUA12-ZEHNER)將混合物薄膜覆蓋到電路上，組件安放在薄膜上。【The composite is prepared by mixing Ag-coated Ni particles with PVA. A thin film of the mixture is applied over the circuit using a thin-film applicator (ZUA12-ZEHNER), and the components are placed over the film】
也可以通過絲網印刷或旋塗將zPVA薄膜沉積到電路上【Alternatively, screen printing or spin-coating can be used to deposit a thin film of the zPVA mixture】
將電路放在磁鐵上，當水從薄膜中蒸發時。通過這種方式，Ag-Ni顆粒將垂直排列，只能在垂直方向上導電。【The circuit is then placed over a magnet, while the water is being evaporated from the film. In this way, the Ag−Ni particles align to form vertical columns that conduct electricity only through the film thickness】
這能用於與柔性電路，微電子組件和其他的PCB板電連接(Figure 2B), Movie S5展示了由LED構成和與其他柔性PCB電連接的電路的轉移處理過程【This can be used to interface flex circuits and
microelectronics components and other PCBs (Figure 2B). Movie S5 shows the transferring process for a circuit populated by light-emitting diode (LED) chips and interfaced with the flexible PCB (FPCB) through zPVA.】
在接觸墊或Ag-Ni顆粒上塗覆一層EGaIn薄膜會進一步改善接觸電阻和機電一體性。【Contact resistance and electromechanical integrity can be further improved by coating the contact pads or Ag−Ni particles with a thin layer of EGaIn】
上述方法制造的電路能夠使用hydrographic transfer (也稱爲 water transfer printing 水轉印，immersion printing )轉移到其他表面上(Figure 2C 和4A)。【Circuits produced with the aforementioned method can be transferred to other surfaces using hydrographic transfer, also referred to as water transfer printing or immersion printing 】
- 首先，將製作完的電路完全進入到水缸中，【First, a host object is fully immersed in a water bath or tank.】
- 接着，“Ag-In-Ga”漂浮在水錶面【Next, the “Ag−In−Ga” circuit is suspended on the surface of a water bath】
- 幾秒後，TTP的水溶性中間層基質溶解，5μm厚的載體薄膜從背紙分離【After some seconds, the watersoluble middle layer of the TTP substrate dissolves and separates the 5 μm carrier film from the backing paper】
- 當物體從水中提出時，載體膜將依附到物體上，並貼合物體表面【The carrier film then clings to the object and conforms to its surface as the object is subsequently lifted out of the water bath.】
由於載體膜很薄，並且具有延伸性，薄膜能夠很緊密的依附表面的形狀，甚至能夠支持180度的自摺疊和彎曲(Figure 4A)【Because it is thin and stretchable, the film is able to follow closely the shape of the surface and can even support 180° self-folding or bending around a thin part】
當從水缸中移除後，電路和基底將被幹燥，轉移之後，可以噴塗一層塑料保護膜密封。【After removal from the bath, the substrate and circuit are allowed to dry. After transfer, the circuit may be spray coated with a protective plastic sea】
基於不同的轉印紙，轉移過程可能有略微不同，比如水紋紙(hydrographic paper)與TTP相比，需要不同的步驟,對於水紋紙而言，載體膜由聚乙烯醇(PVA)和聚醋酸乙烯酯(PVAc)製成，沒有單獨的水溶性層。此時，在浮在水之前需要手動除掉支撐層。【The procedure for the film transfer differs slightly based on the type of the transfer paper used. As an example, the hydrographic paper requires different steps than the TTP — for the hydrographic paper, the carrier film is made out of PVA and polyvinyl acetate (PVAc), and there is no separate water soluble layer. In this case, the backing paper is removed manually prior to floating over water】
除此之外，當與電路結合時，物體表面應從上面靠近薄膜和浸入水中。製作和轉移過程在Movie S1中展示【In addition, the host surface should approach the film from above and enter the water when bonding with the circuit. The fabrication and transfer process is also shown in Movie S1】
使用激光打印機打印測試電路，接下來是Ag和EGaIn沉積。Figure 3A，等寬的線，之間的間隙從50到1000um，被打印，之後是Ag和EGaIn沉積。從圖中可以看出，能夠打印寬度爲200um線。小的線間隙會導致相鄰線之間預想不到的鏈接【In order to establish the patterning resolution, a test circuit was printed using a laser printer, followed by the Ag and EGaIn deposition, as previously described. Referring to Figure 3A, lines with equal width and spacing from 50 to 1000 μm were printed and observed after deposition of Ag epoxy and EGaIn coating. As can be seen in the figure, this technique is able to successfully print lines with a pitch of 200 μm. Smaller spacing resulted in unintended connections between adjacent lines】
Figure 3B，GaIn塗覆的Ag導線在電導率上至少會增加6個數量級。
爲了證實這一現象，測試了激光打印和Ag沉積之後10個樣本的導電率
在沉積EGaIn後，不導電的Ag膠料導線的表面電阻爲0.13 □（10次測量的平均值），在這些樣本中，Ag電路在EGaIn沉積之前在40攝氏度下處理2h。
這樣的話，Ag會粘附在下面的打印墨粉上，多餘的Ag可以使用不起毛的布去掉。或者，Ag膠料可以在室溫下乾燥24h。如果加熱到更高的溫度(比如80攝氏度)，在沉積EGaIn之前電阻爲0.80□，沉積後爲0.16□。
在低溫下乾燥，Ag和打印電路與其他未打印的基底之間的鍵合力有很大的不同。這可以用一塊布使用很輕柔的力，在不損壞電路的情況下除去過量的銀【there is a significant difference between the bonding forces of Ag over the printed circuit and rest of the substrate. This makes it easy to remove the excessive Ag with a piece of cloth and mild mechanical force and without damaging the circuit.】
在更高的溫度下乾燥，會增加Ag與整個基底的鍵合力，需要額外的力，會損壞電路，除此之外，載體薄膜在高溫下回由於熱膨脹而變形，會影響薄膜的基底轉移。【Curing at higher temperature improves the bonding of the deposited Ag with the whole substrate, which makes it necessary to apply an additional force, which can damage the circuit. In addition, at higher temperature, the carrier film deforms through thermal expansion, which affects the subsequent transfer of the film】
爲了測量zPVA中z軸方向的電阻，我們在玻璃上沉積200,300,400um後的薄膜，當乾燥後，從玻璃上玻璃脫落。【In order to characterize the z-axis resistance of zPVA, we deposited films of 200, 300, and 400 μm thickness over glass and then released the film by peeling it from the glass after it dried.】
3mm直接的圓形接觸墊放在薄膜兩端，使用四端子法測量其電阻。Figure 3D展示了10次測量的平均結果。【Two pieces of the flex circuit with round contact pads of 3 mm diameter were placed on both sides of the zPVA film, and the resistance between them was measured with fourterminal sensing. Figure 3D shows average results for 10 measurements】
正如所期望的，電阻隨着厚度增加而增大。
在另一項測試中，我們將200um的zPVA薄膜直接沉積在Cu基底上，乾燥後，之後使用激光圖案化的模板在zPVA薄膜上噴塗直徑3毫米的EGaIn圓(Figure S4)【In another test, we deposited a 200 μm film of zPVA directly over a copper substrate and allowed it to dry. Afterward, we spray-coated 3 mm diameter circles of EGaIn over the zPVA film, using a laser-patterned stencil (Figure S4】
噴塗沉積使用與液體金屬(LM)相似的霧化液滴,使用與文獻30相似的噴塗槍。【LM similar, using a spray gun similar to the method presented in ref 30】
此時Cu−zPVA−Cu的電阻爲0.86,Cu−zPVA−LMd的電阻爲0.57【Within this setup, the average value of z-axis resistance was reduced from 0.86 Ω for the Cu−zPVA−Cu interface to 0.57 Ω for the Cu−zPVA−LM interface (Figure 3E)】
這可以由 Ag覆蓋的Ni例子的數量來解釋，這些顆粒相互連接，在zPVA兩邊形成連續的導電通路。而且由於液體金屬合金填充接口形成更緊密的接觸，電阻會進一步下降。當將Cu基底替換爲導電纖維(Cu-Ni塗覆的無紡布-3M CM-3490)時，電阻減小了約10倍(平均0.03, Figure 3E)【This improvement can be explained by the number of Agcoated Ni particles that are able to connect and form a continuous electrically conductive pathway between the opposite sides of the zPVA film. Such conductivity is aided by the ability of the LM alloy to fill the interface and form a more conformal contact. When replacing the Cu substrate with a conductive fabric (Cu/Ni-coated nonwoven fabric-3M CN- 3490), the resistance of the z-axis interface was further reduced by over a factor of ten (average = 0.03 Ω; see Figure 3E).】
這種戲劇性的降低可以解釋爲鍍鎳導電織物的鐵磁性能，當zPVA在磁鐵上乾燥時，Ag覆蓋的Ni與織物中的Ni形成緊密粘附，促進導電 【This dramatic enhancement can be explained by the ferromagnetic properties of the nickel coating of the conductive fabric. When zPVA is drying over the magnet, the Ag-coated Ni beads can make strong adhesion with the underlying Ni coating, which contributes to better conductivity】
爲了特使電路在機械壓力下的電學表現，做了一系列機電測試(Figure 3F).【In order to characterize the electrical behavior of these circuits under mechanical strain, we performed a set of electromechanical tests (Figure 3F).】
測試包括當受到單軸嚮應變時測量電路的相對電阻。【The test includes measuring the relative resistance of the circuits when subject to uniaxial strain】
一種是在TTP上打印“Ag-In-Ga”，使用上述提到的方法，接着夾在兩個PDMS層中(Figure 3ii),製作的更詳細信息在Materials and Methods中。結果顯示樣本最大可以承受73.1%(std=4.7%)的形變。當與zPVA集成後(Figure 3F(ii))，值降低爲56.7%（std=4.2%）【One set of tests includes samples of printed “Ag−In−Ga” over the TTP, which was prepared by the method referred above, and then sandwiched between two PDMS layers (Figure 3F(ii)). More information on sample preparation can be found in the Materials and Methods section. Results show that “Ag−In−Ga” samples can withstand a maximum strain of 73.1% (std = 4.7%). When integrating zPVA (Figure 3F(iii)), this value reduces to 56.7% (std = 4.2%).】
與預期一樣，由於zPVA和TTP的楊氏模量不同，zPVA試樣的應變率較低。所有的樣本在zPVA處破裂。【As expected, the sample with zPVA breaks at a lower strain rate because of the difference in the Young’s modulus of zPVA and TTP. All these samples broke at the zPVA interface】
在60%的形變下，電阻的變化不算很大(R/=1.5, std=0.22)。這對於可伸縮數字電路是一個大的優勢。【Also, the changes on the resistance of samples against strain is the modest (R/Ro = 1.5, std = 0.22), at 60% strain. This is an important beneficial factor for application in stretchable digital circuits】
最後，“Ag-In-Ga”電路與水接觸時有很強的魯棒性，Figure S3展示了漂浮在水面上的功能性電路。Movie S4展示了將電路浸入水中，當從水中取出時仍具有功能性。【Last, “Ag−In−Ga” circuits are very robust when in contact with water. Figure S3 shows a functional circuit floated on water and Movie S4 shows a circuit that is immersed in a water tank and remains functional after being removed from water.】