Preparation of flexible resistive humidity sensors with different electrode gaps by screen printing and their humidity-sensing properties

Abstract

A novel, flexible resistive-type humidity sensor was fabricated through silk-screen printing of a humiditysensitive copolymer of [2-(methacryloyloxy)ethyl] dimethyl benzyl ammonium chloride and methyl methacrylate on a glass epoxy (GE) substrate. The basic structure of the sensor consisted of a 4-fingered interdigital electrode with various gaps (310, 360, 410, and 460 µm). Gold electrodes GE substrate were prepared by first printing silver nanopaste (thickness 6-7 µm), followed by consecutive electroless plating of Cu (5 µm), Ni (2 µm), and then Au (80 nm). The activation energy for ion conduction and the copolymer/substrate interface were used to explain the differences of humidity-sensing characteristics of sensors fabricated on a GE substrate. Electrode construction had a significant influence on the humidity-sensing characteristics of polymeric relative humidity sensors. Details regarding humidity sensor characteristics, including sensitivity, linearity, temperature dependence, hysteresis, and response time depending on electrode construction were compared. The flexible humidity sensor showed acceptable linearity between logarithmic impedance and relative humidity in the range of 20-95%RH, low hysteresis (within 1.5%RH), good response (75 s) and recovery time (95 s), and long-term stability (225 days at least), measured at 1 V, 1 kHz, and 25 o C.

A Review on Humidity, Temperature and Strain Printed Sensors—Current Trends and Future Perspectives

“…Material selection is of vital importance in sensor performance; conductive electrodes can be printed with Ag [ 11 , 13 , 14 , 15 , 16 ] or PEDOT:PSS [ 17 ] and flexible substrates utilized can be PI (Kapton) [ 10 , 14 , 15 , 18 , 19 ], PET [ 16 , 20 , 21 , 22 ], polyester-based [ 23 , 24 ], paper [ 12 , 17 ]; or rigid, such as glass [ 25 ] or ceramic [ 26 ]; this is directly correlated to the printing technique. A hybrid approach has been proposed by numerous research groups, where the conductive electrodes are not printed but traditionally patterned and the sensing layer is printed on top [ 19 , 26 , 27 , 28 ].…”

“…Humidity sensors nominally share a common strategy: electrode deposition with a printing technique such as inkjet [ 12 , 17 , 20 , 35 , 36 , 39 , 40 , 45 ], screen [ 10 , 13 , 15 , 16 , 21 , 24 , 25 , 32 , 43 ] or gravure [ 14 , 38 , 44 ], or a traditional process such as lithography [ 26 , 27 , 28 , 37 ], followed by a sensing layer deposition either via inkjet [ 22 , 23 , 40 ], screen [ 15 , 18 , 25 , 32 , 43 ], gravure [ 10 , 13 , 16 , 21 , 44 ], spin coating [ 27 , 28 , 37 , 38 ] or drop casting [ 14 , 19 , 26 ]. Some groups have presented an approach where the substrate acts as a sensing layer [ 12 , 17 , 34 , 35 , 36 , 45 , 87 ] thus eliminating the need for an additional step of deposition of such layer, while humidity sensors can either provide a resistive...…”

AC Complex Impedance Study on the Resistive Humidity Sensors with Ammonium Salt-Containing Polyelectrolyte using a Different Electrode Pattern

“…However, the main drawback was the small variations in their intrinsic resistances; the variations were so small that no significant difference was detected between the samples. 26,27 Therefore, it is necessary to measure other electrical properties of the sensor to maximize sensitivity so that the AC complex impedance characteristics can be investigated when assessing a humidity sensor with different electrode configurations.…”

The Progress of Research into Flexible Sensors in the Field of Smart Wearables

“…Due to the various preparation methods of conductive materials, they have greater compatibility with different substrate materials. For example, a wide range of processes, such as dip coating, in situ assembly, mechanical press, transfer printing technology, and chemical deposition, etc., can be used to combine with the substrate [ 9 , 10 , 11 , 12 ]. Cyclic stretching or compression is usually used to test the selection of a suitable polymer matrix to design a special conductive network to stabilize the conductive network, so that the sensitive components have a stable sensing behavior.…”