Low Operating Voltage and Highly Pressure-Sensitive Printed Sensor

Article Cite This: ACS Appl. Electron. Mater. XXXX, XXX, XXX−XXX

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Low Operating Voltage and Highly Pressure-Sensitive Printed Sensor for Healthcare Monitoring with Analogic Amplifier Circuit Tomohito Sekine,*,† Alexandre Gaı̈tis,‡ Jun Sato,† Kohei Miyazawa,† Kosuke Muraki,† Rei Shiwaku,† Yasunori Takeda,† Hiroyuki Matsui,† Daisuke Kumaki,† Fabrice Domingues Dos Santos,§ Atsushi Miyabo,∥ Micaël Charbonneau,‡ and Shizuo Tokito*,†

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†

Research Center for Organic Electronics (ROEL), Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan ‡ CEA Liten, 17, Avenue des Martyrs, Grenoble 38054, France § SCB#3, Kyoto Research Park, 93 Chudoji Awatacho, Shimogyo-ku, Kyoto 600-8815, Japan ∥ Arkema K. K., 93, Chudoji, Awatacho, Shimogyo, Kyoto 600-8815, Japan S Supporting Information *

ABSTRACT: Flexible printed analogic amplifier circuits are required in wearable sensors to enhance their sensitivity for application in various fields such as healthcare, artificial skins, and soft robotics. Various technologies have been proposed to develop wearable sensors for healthcare. However, the development of piezopolymer-based printed healthcare devices for monitoring human vital signs that simultaneously achieve high sensitivity and low operating voltage remains a challenging task. Here, a highly pressure-sensitive printed sensor with low operating voltage is demonstrated and applied to monitor human pulse wave velocity (PWV). The printed sensor consists of a 2 μm thick pressure detector and an organic analogic amplification circuit that are simultaneously formed on flexible substrates. The printed organic analogic circuit can amplify the generated signal by a gain factor of 10. This configuration makes it possible to combine good pressure sensitivity (∼10 kPa) with a low operating voltage of −3 V. We attached the sensor on the skin to efficiently monitor human vital signs using PWV to estimate health conditions. KEYWORDS: wearable sensor, printed analogic circuit, pulse wave measurement, ferroelectricity, low voltage operating

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INTRODUCTION The development of flexible and bendable sensors for pressure monitoring has various potential applications in wearable electronics, artificial skins, and soft robotics.1−10 For these applications, the conventional sensors are unsuitable due to low bendability from their rigid material components. In recent years, various technologies have been proposed to use wearable pressure sensing in healthcare monitoring systems such as flexible pressure sensors with microstructured rubber dielectric layers,11 a highly sensitive pressure sensor with ultrathin gold nanowires,12 and a conductive fiber-based textile pressure sensor.13 Recently, a new approach as the concept of “piezoelectric polymeric sensor for human vital sign sensing” has been proposed, where ferroelectric polymers are fabricated on a plastic substrate adaptable to wearable sensors. This concept has advantages such as flexibility, high pressure sensitivity, and fast response time and can be driven without a power source, compared with previous sensors.14 In addition, the designability of the sensor devices is extremely high, because the above materials can be adopted to printing technologies.15 For © XXXX American Chemical Society

instance, Ziekl et al. reported a sensor network by using a piezoelectric polymer and various printing materials. This work indicated a smart sensor with low cost.16 Fujita et al. reported a flexible sensor for monitoring vital human signs by using poly(vinylidene fluoride) (PVDF) copolymer material.17 This material is usually useful for a dielectric layer such as thin-film transistors.18,19 In this study, the vital signs were amplified by an inorganic-type operational amplifier. From another perspective, Boroujeni et al. fabricated an audio amplifier circuit with polymeric materials on a flexible substrate.20 They used printing processes to fabricate a circuit to amplify the signal generated by a piezopolymer. The above-mentioned piezoelectric systems are considered to be highly significant for the realization of wearable sensors to monitor human vital signs. Received: December 3, 2018 Accepted: February 5, 2019 Published: February 5, 2019 A

DOI: 10.1021/acsaelm.8b00088 ACS Appl. Electron. Mater. XXXX, XXX, XXX−XXX

Article

ACS Applied Electronic Materials

Figure 1. Schematic design of device fabrication of a flexible and highly pressure-sensitive printed sensor. (a) The fabrication steps of our printed pressure sensor and its device structure. (b) Magnified view of our printed pressure sensor in the flexible state. (c) Schematic circuit diagram of our sensor. The blue and red dotted lines identify P(VDF-TrFE) as the piezoelectric component and the amplifier circuit, respectively.

for improvement of their amplification ability. Other studies achieved an operating voltage of approximately −20 V.20 In addition, other limitations of pressure sensors that include an amplifier circuit to read out signals from detectors are their complicated fabrication processes and high-power consumption.24 Therefore, printed and low operation devices will solve the above challenging tasks by providing high sensitivity and low operating voltage. Here we demonstrate a printed sensor that is highly pressure-sensitive yet has an extremely low operating voltage and its application for monitoring human pulse wave veracity. A 2 μm thick pressure detector and organic analogic amplification circuit were simultaneously formed on flexible substrates, which can be almost imperceptibly attached to the skin because of its light mass of 1.5 g. The printed detector can accurately measure pressure lower than 10 kPa. Moreover, the printed organic analogic circuit, which consists of organic thinfilm transistors connected with the Darlington connection method, can amplify the signals generated by the detector by a gain factor of 10. This configuration ensures the compatibility of high-pressure sensitivity (∼10 kPa) and fast response time (∼0.1 s) with a low operating voltage of −3 V. The above advantageous features enable our sensor to easily monitor human vital signs using pulse wave velocity (PWV) to estimate health conditions by attachment to the skin. The calculated PWV value was approximately 9 m·s−1, which is not inferior compared with the value obtained with existing meters for that parameter. The mentioned operating voltage is extremely low and excellently suited to a patch-type pressure sensor.

The relation of piezoelectricity can be explained by combining Hooke’s Law and the electrical behavior of the material as given in the following equations21 S = s ET + dE

(1)

D = dT + εT E

(2)

where S is the strain, s is compliance, and T and d are applied stress and the piezoelectric constant. D is the displacement of the electric charge density, ε is permittivity, and E is the electric field strength. The signal Vgen generated with pressure P by the piezopolymers, such as PVDF, depend on their film thickness, as expressed by Hooke’s law and eq 3 as follows Vgen =

ad33Pt ε0ε

(3)

where a is a proportional constant, d33 is the piezoelectric constant of the piezopolymer, t is the thickness of the piezopolymer, and ε0 is the permittivity of piezopolymer materials. Here, the piezopolymer-based sensors preferably need to have reduced thickness because of the need to directly attach the wearable sensor to the skin without creating the feeling that the sensor is fitted.22,23 These trends are similar for printed devices. Thus, amplification is important for a piezopolymeric printed pressure sensor.24 However, fabricating printed healthcare devices to monitor human vital signs, devices that simultaneously achieve high sensitivity, reliability, and low operating voltage, remains a challenging task. In fact, the major obstacle to overcome is the high operating voltage required by pressure detectors and circuits. In addition, the gain factor of a printed analogic circuit is low. In particular, low operating voltage has not previously been achieved, because the detector devices of these sensors usually require an operating voltage exceeding 10 V. Reducing the operating voltage to less than 10 V is possible, because wearable power sources such as flexible rechargeable lithiumion batteries have been achieved with an output voltage below 10 V.25 Moreover, as mentioned previously, printed analogical circuits have a gain factor of 2, which shows that there is room

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RESULTS AND DISCUSSION Schematic cross-sectional images and an overview of the fabricated sensor device are shown in Figure 1a,b. The device consists of a pressure detector and an organic amplifier circuit. The key elements and concept are the ferroelectric polymer, poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)]. It shows excellent sensitivity and responds rapidly to applied pressure. Figure 1c shows the electric circuit diagram of the B


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Figure 2. Characteristics of the P(VDF-TrFE) polymeric layer as a pressure detector. (a) Chemical structure of P(VDF-TrFE). The monomer ratio of VDF/TrFE was 75:25. (b) Surface AFM images of the P(VDF-TrFE) layers after annealing. The annealing temperatures were (left) 80, (middle) 140, and (right) 160 °C. Scale bar: 100 nm. (c) Relative changes in output voltage as a function of applied pressure. (d) Flexibility of ferroelectric parameters of the P(VDF-TrFE) layer. Applied maximum strain was 1%. P(VDF-TrFE) thickness was 2 μm.

Figure 3. Characteristics of the analogic amplifier circuit with the printed OTFTs. (a) Image providing an overview of the printed OTFT in the vicinity of a channel. Scale bar: 50 μm. (b) Surface AFM image of the organic semiconducting layer in the OTFT device. Scale bar: 500 nm. (c) Transfer characteristics of the OTFT devices in the analogic amplifier circuit.

displays the strain sensitivity of the P(VDF-TrFE). Changes in the polarization and electric field are a modicum of approximately 5.0% over 0.6% strain. Generally, output voltage from a piezofilm is in direct proportion to their thickness. Thus, this linearity of the output voltage is reasonable. These results show that the detector has high flexibility and conformability for use in wearable devices. The voltage generated by the applied pressure is plotted in Figure 2d and indicates an explicitly linear relationship on the pressure. This is significant, because it shows that the vital sensor is sensitive to below 10 kPa (inset graph in Figure 2d); thus, the sensor has enough sensitivity for detecting the human pulse rate and exhibits satisfactory pressure sensitivity.26,27 Moreover, as the annealing temperature substantially affects the pressure sensitivity, optimization of the annealing temperature of the printed P(VDF-TrFE) layer is an important aspect of this study (Figures S3 and S4). The ability of a printed organic circuit to perform effectively as an amplifier is determined by measuring several printed OTFTs. Our analogic amplifier circuit consisted of three printed OTFTs, a chip-typed resistance (100 MΩ), and a condenser (1 μF). Figure 3a shows an overview of the channel part of a printed OTFT. The material for the organic semiconducting layer was DTBDT-C6. In particular, a high

sensor. The components are the pressure detector, organic thin-film transistors with the Darlington connection, resistance, and capacitor. This connection method is a simplified amplifier system for our sensor devices on an analog circuit. The printed P(VDF-TrFE)-based detector can sense pressure with a nonelectric source because of its ferroelectric properties. Moreover, this sensor comprising organic analogic circuits can operate at only −3 V. The detector generates voltage when pressure is applied, and the voltage is amplified by the organic analogic circuit. The sensor, including the detector and analogic circuit, is lightweight and only weighs 1.5 g. Figure 2a shows the chemical structure of P(VDF-TrFE). The surface atomic force microscopy (AFM) images and ferroelectric hysteresis curves with changing annealing temperature are shown in Figure 2b, in which it can be seen that the surface smoothness and ferroelectricity are compatible below 140 °C. Details of the dependence of the annealing temperature can be found in the Supporting Information. Experimental details of the crystal structure and thermal properties were obtained by using X-ray diffraction (XRD) and differential scanning calorimetry (DSC) and are shown in Figures S1 and S2. The dependence of ferroelectricity and surface morphology of the P(VDF-TrFE) layer on the annealing temperature could be clearly observed. Figure 2c C


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generated in the positive side when pressure was applied to the detector (pressure-on) shown in Figure 4 on the left side. The right side of Figure 4 shows a piezoresponse of 0.11 V with the detector and amplifier circuit. We achieved amplification of the signal from the detector by a factor of approximately 10. These results clearly correspond with the designed gain factor of the circuit. The pressure sensitivity of the printed detector was evaluated by measuring the piezoelectric response by applying pressures ranging from 10 to 100 kPa (Figure 4b). On the pressure, the generated voltage shows a linear dependence with and without the amplifier circuit. Figure 4c shows the pressure sensor including the pressure detector and amplifier circuit during the pressure test, during which its conductivity showed good recovery. This behavior can be seen in the enlarged inset, in which the signal generated near the 100th and 500th cycles is shown. The insignificant changes in the generated signal of the sensor most likely originated from the negligibly small decrease in the polarization value of the P(VDF-TrFE) formed during the pressure test (Figure S8). We demonstrated the high functionality of the printed pressure sensors and their fidelity for PWV measurements by attaching the sensors to the skin of a human adult (Figure 5), as is usually the case in arterial tonometry. The fast response time and high sensitivity of the sensor are suitable for cardiovascular monitoring of PWV monitoring. Monitoring of the velocity of the carotid-femoral pulse wave is usually employed as a standard concept measurement of a health condition. In addition, it can directly correlate to hypertension.30 The PWV means the speed of the blood pulse wave proceeds in arteries.31 The fabricated sensors and a reference monitoring component of an electrocardiogram (ECG) were attached to the skin of the neck and the wrist of the as shown in Figure 5a,b. As shown in Figure 5b, our sensor was attached

degree of smoothness and crystallinity were achieved in the organic semiconducting layer. Figure 3b shows an AFM image of the surface and the structure of the molecule intended as an organic semiconductor. The ability of the OTFTs to operate at extremely low voltage can be attributed to the properties of the semiconducting ink blended with the soft polymeric material polystyrene (PS). This method is finely tunable and reproducible in terms of improving the field-effect mobility and turn-on voltage.28,29 Detailed information on the surface roughness and crystallinity of the blended semiconducting layer can be found in the Figure S5. The transfer characteristics of the OTFTs as components of the amplification circuit are displayed in Figure 3c. Particulars of their characteristics can be found in Table 1. The mobility of all of the OTFTs Table 1. Characteristics of Printed OTFT Devices OTFT1 OTFT2 OTFT3

L (μm)

μ (cm2·V−1·s−1)

Vth (V)

31 32 30

1.01 0.98 1.11

−0.56 −0.17 −0.37

exceeded 1.0 cm2·V−1·s−1, which is sufficient for the analogic amplifier circuit. In fact, simulation with LT Spice software clarified that a mobility of 1.0 cm2·V−1·s−1 and a Vth shift within 0.5 V would be required in all of the OTFTs to accomplish a gain factor of 10 (Figure S6). This showed that our printed OTFTs are useful as one of main elements of the analogic amplifier circuits. Mechanical reliability of the fabricated OTFTs can be found in Figure S7. The piezoelectric response of the detector is shown in Figure 4a (applied pressure: 100 kPa). The operating voltage of the printed circuit was −3 V. Voltage peaks of 0.01 V were

Figure 4. Amplifying ability of the analogic circuit for the P(VDF-TrFE)-based pressure detector. (a) Piezoelectric response of the sensor for the pressure: (left) P(VDF-TrFE) layer only, (right) with the analogic amplifier circuit. The applied pressure was 100 kPa, and the detecting area was 1.5 mm2. (b) Changes in the generated voltage for the pressures with and without the amplifier circuit for the P(VDF-TrFE) layer. (c) Real-time recording of output voltages of the printed sensor for the ferroelectric property during the cycling process. D


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Figure 5. Human pulse wave monitoring of the artery of the neck and wrist with our sensor and PWV monitoring. (a) Setup for monitoring the human PWV and velocity with our sensors and ECG unit, which were attached to the skin of a human using an adhesive patch. (b) Magnified view of the sensor attached to the human wrist. Sensor 1 was attached on the neck, and sensor 2 was attached on the wrist. (c) Positions at which human PWV was monitored by measuring signals from the neck and wrist. The distance between sensors 1 and 2 and Δt were 90 cm and 0.1 s, respectively. (d) Real-time signals monitored from the blood flow and electrocardiograph using our sensors and the ECG unit. (e) Magnified view of the monitored pulse wave signal using sensor 1. (f) Comparison of signal shape of the pulse wave using our sensor and the piezoresistance-based sensor.

fabricated by using printing processes. The pressure-detecting ability of the sensor was improved by optimizing the annealing processes. Moreover, the improved detector was able to measure faint pressure below 10 kPa, thereby surpassing the other P(VDF-TrFE)-based printed pressure sensors. The organic analogic circuit amplifies the signal generated by the detector, which requires an operating voltage of only −3 V, and this was achieved by improving the crystallinity and fieldeffect mobility of the semiconducting material. To demonstrate their feasibility for monitoring vital human signals, the sensors were implemented in a wearable healthcare device. Despite the low operating voltage of the sensors, they were capable of successfully monitoring human pulse waves. These waves are an indication of the PWV (9 m·s−1 in this case) as a clear demonstration of the health condition of the volunteer.

above the positions, and the arterial wave was monitored. Furthermore, the ECG was simultaneously used as reference of a time record. The PWV was calculated with the following formula32,33 PWV (m·s−1) =

d Δt

(4)

We then calculated the PWV to be 9 m·s−1 via the time delay between the pulse signal in the neck and wrist (in Figure 5c). In Figure 5e, the position of the baseline of the pulse wave is also indicated. Additionally, it shows an extended view of a pulse wave with the characteristic peaks typically measured at the radial artery.34,35 In this paper, the size of the pressure detector was 20 mm. When we measure the human pulse wave, it is to be desired that the size is wider than diameter of a human bezel. Finally, we monitored the human pulse wave of the volunteer by using our printed sensor and a piezoresistance-type pressure sensor (Inastomer, Inaba Rubber. Co. Ltd.,). Our sensor responds rapidly to applied pressure and can detect human vital signs with accuracy. In particular, in contrast to a piezoresistance-type pressure sensor, our sensor can clearly monitor the medical care parameters P1 and P2, which lead to blood vessel hardness in humans.

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EXPERIMENTAL SECTION

Sensor Fabrication. The printed highly sensitive pressure sensor is based on a pressure detector and an amplifier circuit. A planarization layer was fabricated on a poly(ethylene naphthalate) (PEN) film substrate (Q65HA, 50 μm, DuPont). A cross-linked poly(4-vinylphenol) (PVP) (436224, Sigma-Aldrich) solution mixed with the PVP and 1-methoxy-2-propyl acetate (Kanto Chemicals 01948−00) as the solvent was formed by spin-coating onto the PEN film as the planarization layer. The lower and upper electrodes of the pressure detector were formed using PEDOT:PSS (Clevious SV4 STAB, Heraeus) on the substrate by screen printing (MT320T, Microtech, Japan) and annealing at 140 °C for 30 min. The thickness of the layer was 500 nm. Next, P(VDF-TrFE) (Piezotech, molar ratio of VDF/TrFE is 75:25, 2000 nm) was formed by screen printing and annealing at 140 °C for 1 h. The P(VDF-TrFE) was dissolved in

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CONCLUSION In conclusion, we developed a printed sensor that requires low operating voltage and is highly pressure-sensitive for human healthcare monitoring; the sensor response to applied pressure is fast, and it can detect human vital signs with accuracy. This sensor is flexible, lightweight, and cost efficient, because it is E


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ACS Applied Electronic Materials cyclohexanone at concentrations of 10 wt %. Next, silver nanoparticle ink (Harima Chem. NPA-JL) was patterned as a gate electrode by inkjet printing (Fujifilm Dimatix, model DMP2831), after which it was annealed at 140 °C for 1 h.36 As a gate dielectric layer, 200 nm thick parylene (KISCO, diX-SR) was then formed by chemical vapor deposition. The dielectric constant of the parylene was 3.1. Next, the silver nanoparticles were patterned by inkjet printing, forming the source and drain (S and D) electrodes. The L and W (length and width) of the channel of OTFTs were 30 and 10 000 μm, approximately. A self-assembled monolayer (SAM) for the S/D electrodes was formed by immersing the specimen in a propanol solution (3 × 10−2 mol/L) of pentafluorobenzenethiol (PFBT) for 5 min at room temperature. Bank layers (DuPont, Teflon, AF1600) were formed by the dispenser (MUSASHI Engineering, Image Master 350 PC) at a pattering speed of 20 mm·s−1. As the final process, the organic semiconducting layer was printed. A solution of dithieno[2,3d;2′,3′-d′]benzo[1,2-b;4,5-b′]dithiophene (DTBDT-C6) (TOSOH Co., Japan) (1.0 wt %) and polystyrene (0.25 wt %, Sigma-Aldrich) blends in toluene was formed onto the channel area by the dispenser at a patterning speed of 20 mm·s−1. Then, the substrates were stored in ambient air for 10 min. Last, a 200 nm thick passivation layer was formed by parylene. After fabrication of the sensor device, each pair of drain and gate electrodes were connected using conductive silver paste.

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like to thank Editage (www.editage.jp) for the English language review.

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(1) Lu, N.; Lu, C.; Yang, S.; Rogers, J. Highly Sensitive SkinMountable Strain Gauges Based Entirely on Elastomers. Adv. Funct. Mater. 2012, 22, 4044−4050. (2) Yao, S.; Zhu, Y. Wearable Multifunctional Sensors Using Printed Stretchable Conductors Made of Silver Nanowires. Nanoscale 2014, 6, 2345−2352. (3) Gao, W.; Emaminejad, S.; Nyein, H. Y. Y.; Challa, S.; Chen, K.; Peck, A.; Fahad, H. M.; Ota, H.; Shiraki, H.; Kiriya, D.; Lien, D.-H.; Brooks, G. A.; Davis, R. W.; Javey, A. Fully Integrated Wearable Sensor Arrays for Multiplexed in situ Perspiration Analysis. Nature 2016, 529, 509−514. (4) Yamamoto, Y.; Yamamoto, D.; Takada, M.; Naito, H.; Arie, T.; Akita, S.; Takei, K. Efficient Skin Temperature Sensor and Stable GelLess Sticky ECG Sensor for a Wearable Flexible Healthcare Patch. Adv. Healthcare Mater. 2017, 6, 1700495−1700502. (5) Wang, C.; Hwang, D.; Yu, Z.; Takei, K.; Park, J.; Chen, T.; Ma, B.; Javey, A. User-Interactive Electronic Skin for Instantaneous Pressure Visualization. Nat. Mater. 2013, 12, 899−905. (6) Kim, J.; Lee, M.; Shim, H.; Ghaffari, R.; Cho, H. R.; Son, D.; Jung, Y. H.; Soh, M.; Choi, C.; Jung, S.; Chu, K.; Jeon, D.; Lee, S.-T.; Kim, J. H.; Choi, S. H.; Hyeon, T.; Kim, D.-H. Stretchable Silicon Nanoribbon Electronics for Skin Prosthesis. Nat. Commun. 2014, 5, 5747−5758. (7) Kim, K. N.; Chun, J.; Kim, J. W.; Lee, K. Y.; Park, J.-U.; Kim, S.W.; Wang, Z. L.; Baik, J. M. Highly Stretchable 2D Fabrics for Wearable Triboelectric Nanogenerator under Harsh Environments. ACS Nano 2015, 9, 6394−6400. (8) Matsuhisa, N.; Inoue, D.; Zalar, P.; Jin, H.; Matsuba, Y.; Itoh, A.; Yokota, T.; Hashizume, D.; Someya, T. Printable Elastic Conductors by in situ Formation of Silver Nanoparticles from Silver Flakes. Nat. Mater. 2017, 16, 834−842. (9) Harada, S.; Kanao, K.; Yamamoto, Y.; Arie, T.; Akita, S.; Takei, K. Fully Printed Flexible Fingerprint-Like Three-Axis Tactile and Slip Force and Temperature Sensors for Artificial Skin. ACS Nano 2014, 8, 12851−12857. (10) Park, J.; Lee, Y.; Hong, J.; Ha, M.; Jung, Y.-D.; Lim, H.; Kim, S.Y.; Ko, H. Giant Tunneling Piezoresistance of Composite Elastomers with Interlocked Microdome Arrays for Ultrasensitive and Multimodal Electronic Skins. ACS Nano 2014, 8, 4689−4697. (11) Mannsfeld, S. C. B.; Tee, B. C.-K.; Stoltenberg, R. M.; Chen, C. V. H.-H.; Barman, S.; Muir, B. V. O.; Sokolov, A. N.; Reese, C.; Bao, Z. Highly Sensitive Flexible Pressure Sensors with Microstructured Rubber Dielectric Layers. Nat. Mater. 2010, 9, 859−864. (12) Gong, S.; Schwalb, W.; Wang, Y.; Chen, Y.; Tang, Y.; Si, J.; Shirinzadeh, B.; Cheng, W. A Wearable and Highly Sensitive Pressure Sensor with Ultrathin Gold Nanowires. Nat. Commun. 2014, 5, 3132. (13) Lee, J.; Kwon, H.; Seo, J.; Shin, S.; Koo, J. H.; Pang, C.; Son, S.; Kim, J. H.; Jang, Y. H.; Kim, D. E.; Lee, T. Conductive Fiber-Based Ultrasensitive Textile Pressure Sensor for Wearable Electronics. Adv. Mater. 2015, 27, 2433−2439. (14) Lou, Z.; Chen, S.; Wang, L.; Jiang, K.; Shen, G. An UltraSensitive and Rapid Response Speed Graphene Pressure Sensors for Electronic Skin and Health Monitoring. Nano Energy 2016, 23, 7−14. (15) Haque, R. I.; Vié, R.; Germainy, M.; Valbin, L.; Benaben, P.; Boddaert, X. Inkjet Printing of High Molecular Weight PVDF-TrFE for Flexible Electronics. Flex. Print. Electron. 2016, 1, 015001− 015012. (16) Zirkl, M.; Sawatdee, A.; Helbig, U.; Krause, M.; Scheipl, G.; Kraker, E.; Ersman, P. A.; Nilsson, D.; Platt, D.; Bodö, P.; Bauer, S.; Domann, G.; Stadlober, B. An All-Printed Ferroelectric Active Matrix Sensor Network Based on Only Five Functional Materials Forming a Touchless Control Interface. Adv. Mater. 2011, 23, 2069−2074. (17) Fujita, T.; Shiono, S.; Kanda, K.; Maenaka, K.; Hamada, H.; Higuchi, K. Flexible Sensor for Human Monitoring System by using P(VDF/TrFE) Thin Tilm. 2012 5th International Conference on

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsaelm.8b00088.

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REFERENCES

Figures S1 and S2 show the X-ray diffraction pattern and DSC heating curve. Figure S3 shows the ferroelectric hysteresis loops of P(VDF-TrFE)-based pressure detector. Figures S4 and S5 show polarization of P(VDF-TrFE) and detailed information on surface roughness and crystallinity of the blended semiconducting layer. Figures S6 and S7 show simulation of amplifier ability of our sensor and mechanical reliability of the fabricated OTFT devices. Figure S8 shows ferroelectric characteristics in the cycle test (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (T.S.) *E-mail: [email protected] (S.T.) ORCID

Tomohito Sekine: 0000-0002-2821-1104 Notes

In this manuscript, demonstrations involved a volunteer with approval from the institutional review board of Yamagata University (no. 30−6). Consent was obtained from the authors and volunteer specifically for the purpose of including the information in a publication. The authors confirmed that all experiments were performed in accordance with the relevant guidelines and regulations of the institutional review board. The authors declare the following competing financial interest(s): DTBDT-C6 was provided by TOSOH Corporation at no charge. There are no other competing financial interests in this work.

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ACKNOWLEDGMENTS This study was partially supported by the Japan Science and Technology Agency (JST), Foundation for Technology Promotion of Electronic Circuit Board. The authors would F


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Low Operating Voltage and Highly Pressure-Sensitive Printed Sensor

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