Graphene-Based Three Dimensional Capacitive Touch Sensor for Wearable Electronics

Transcription

1 Supporting Information Graphene-Based Three Dimensional Capacitive Touch Sensor for Wearable Electronics Minpyo Kang, Jejung Kim, Bongkyun Jang, Youngcheol Chae, Jae-Hyun Kim and Jong-Hyun Ahn, * School of Electrical and Electronic Engineering, Yonsei University, Seoul 03722, Republic of Korea. Department of Nano Mechanics Nano Convergence Mechanical Systems Research Division, Korea Institute of Machinery & Materials, Daejeon 34103, Republic of Korea. * Corresponding author: ahnj@yonsei.ac.kr 1

2 Supplementary Note 1: Calculation of Signal-to-Noise Ratio (SNR) SNR (db) = 20 log STouch (1) NTouch RMS100 STouch = Signal Touch,AVG100 Signal Untouch,AVG100 (2) Signal Touch,AVG100 = 99 n=0 Signal Touch[n] 100 (3) Signal Untouch,AVG100 = 99 n=0 Signal Untouch[n] 100 (4) NTouch RMS100 = 99 n=0 (Signal Touch [n] Signal Touch,AVG100) (5) SNR is a measured amount used in touch sensor controllers that is commonly accepted as an industry-wide standard. Especially in capacitive touch sensors, the signal in SNR is directly related with sensitivity of device performance. The SNR of touch sensor can be modeled using equation (1), where STouch is the touch strength from equation (2) and NTouch is the standard deviation of the signal in (5). In equation (3) and (4), Signal Touch is the touch signal level and Signal Untouch is the untouched signal level. 2

3 Supplementary Note 2: Calculation of strain level for each layer The bending strain of i th layer in a composite beam is calculated based on Eulerian beam theory by where y i = central position of i th layer measured from the bottom surface of the composite beam, and ρ = radius of bending. The location of the neutral surface y c is calculated by (1). (2) 3

4 Figure S1. Strain values of each layer in various bending radius. The blue vertical line indicates the bending radius of 1.5 mm. 4

5 Figure S2. Mechanisms of touch and proximity sensor detection. 5

6 Figure S3. Response time of touch sensor. 6

7 Figure S4. Stability test for 200 cycles. 7

8 Figure S5. Ground shielding effect of touch panel on skin. The response of touch sensors (a) with ground shielding layer and (b) without ground shielding layer. 8

9 Figure S6. Ground shielding effect of touch panel. When the solution which has similar properties of sweat (1% NaCl) was put under the sensor, capacitance was stable for the droplet. 9

10 Figure S7. Capacitance variation against temperature and humidity. (a) Relative capacitance change (ΔC / C 0 ) versus temperature between 30 and 60 C. (b) Relative humidity between 30 and 60 %. 10

11 Figure S8. 3D tracking of the conductive iron sphere as it moves from left to right above the sensor. The distance between the iron sphere and sensor is 5 mm. 11

12 Figure S9. 3D modeling measurement system and the conductive objects such as (a) iron ball which diameter is 3.5 cm, (b) ring shaped metal which has 4 cm outer diameter and (c) cone shaped metal which has 6.8 cm diameter and 9.5 cm height. All objects were 5 mm apart from the sensor. Scale bar, 2 cm. 12

13 Figure S10. 3D sensing of stretchable touch sensor mounted on palm. (a) iron sphere and (b) cone. The distance between objects and sensor is 5 mm. Scale bar, 1cm. 13

14 Figure S11. Device structure of mesh type capacitive sensor. Blue and red lines indicate bottom and top electrodes respectively. 14

15 Figure S12. End-to-end line resistance of pristine graphene and TFSA doped graphene electrode with respect to the number of layer. The width and length of electrode line are 3 mm and 4 cm, respectively. 15

16 Table S1. Mechanical properties and thickness of constituent materials of 3D touch sensor for finite element analysis (FEA). Table S2. Comparison of the response time of touch sensors. Movie S1 The movie shows the wearable touch sensor mounted on an arm. The device successfully shows three representative operation modes including multi-touch, spread, and scroll, which are essential for controlling conventional smartphones. Movie S2 The movie shows controlling the movement of a toy car by simple finger motion. This device could be controlled by four buttons for different actions, including moving forward, rotating clockwise, rotating counter-clockwise, and stopping. The toy car was controlled by wireless system using Arduino. 16