2012 IEEE 18th

International Symposium for Design and Technology in Electronic Packaging (SIITME)

978-1-4673-4760-0/12/$31.00 ©2012 IEEE 77 25-28 Oct 2012, Alba Iulia, Romania

Capacitive structures produced by printing technology

Brodeala Andreea, Alexandru Vasile, Paul Svasta

“Politehnica” University of Bucharest, Romania andreea.brodeala@cetti,.ro

Ana Aragonez Alcade, Eloi Ramon

Autonomous University of Barcelona, CAIAC UAB, 08193 Bellaterra, Barcelona,

Abstract — The experiments presented here aim at achieving

capacitor structures of different sizes, but fabricated with the

same materials and measured under the same conditions. For

printing the conductive part, the silver ink SunTronic EMD 5603

was used. For the dielectric poly-4-vinylphenol (PVP - is a water

soluble polymer) was used. The aim was to obtain a structure of

two capacitors, in series, on flexible substrate. Printed routes are

arranged in the shape of a pyramid, from small to large, so that

connections to PVP cannot join. After printing each layer, the

structure was subjected to heat treatment to evaporate solvents

from inks and for fixing the layers. The measured capacity, from

these structures, of the devices ranges from 560 pF to 3nF.

Index Terms— capacitive, structures, printing, technology

I. INTRODUCTION

Organic electronics, new field the stage advanced research institutes and laboratories of large companies producing electronic components, propose new ways of electronic components and circuits including the realization method of inkjet printing using organic materials on flexible substrates. Printed capacitors on flexible substrates can be fabricated using a variety of organic materials, as reported in [1], and have several characteristics that are difficult to obtain with their classical inorganic counterparts [2]. The capacitive structures can be manufactured through various fabrication techniques such as inkjet and screen printing, coating, evaporation or roll-to-roll and they have several useful advantages such as simplicity of fabrication, volatility, the possibility to choose from a variety of substrates and low cost [3]. In this paper, the aim was to use a flexible substrate and ink-jet printing, an additive fabrication technique.

Inkjet technology is a non-contact process because it eliminates the possibility of contamination where different materials are deposited selectively resulting in better operating performance printed materials. Another advantage is to produce fine patterns with smaller financial investment than in the photo-lithography technology, etching and vacuum deposition. Recently there have been significant efforts to achieve the flexible electronic 3D system integration of various passive components such as capacitors, resistors and inductors in multilayer ceramic package [3,4].

Method piezoelectric inkjet printing is the method used in this paper, straw is generated by deforming a piezoelectric element, following the deformation occurs when the pressure

in the room, which eventually resulted in a drop of ink ejection. One laboratory printers was designed to be able to test with their applicability piezo inkjet technology for new processes and production processes, is Dimatix 2800.

Volume droplets deposited on substrate with Dimatix 2800 can be 1pl or 10 pl. From this relatively small droplet size can conclude that printed image composed of pixels is relatively small and therefore can get printed structures with a relatively high resolution. The print head of Dimatix printer which is represented schematically in Fig. 1, has 16 nozzles, where each nozzle is formed as a square of 21.5 microns. These nozzles are arranged side by side in a row, each nozzle being at a distance of 254 microns from the next.

Fig. 1 Dimatix printhead

Home ownership inks used in printing technique is their viscosity in order to be milli Pascal / sec, a reasonable value can be achieved by dissolving any polymer conjugate. printer ink deposited on the substrate dropwise. Printer's print head nozzles are arranged Dimatix one line. to activate the software can print one, two or more jets, depending on the state printhead and ink viscosity.

II. MATERIALS USED IN THIS PAPER

A. Silver ink EMD5603

The ink used for the present work is a Jettable Silver from SunTronic and it is a solvent based silver nano-particle inkjet ink, suitable for printing conductive lines and features in printed electronics and related applications. SunTronic Solsys Jettable Silver can be jetted through various piezo Drop On

2012 IEEE 18th

International Symposium for Design and Technology in Electronic Packaging (SIITME)

978-1-4673-4760-0/12/$31.00 ©2012 IEEE 78 25-28 Oct 2012, Alba Iulia, Romania

Demand inkjet printheads, although full printhead compatibility will need to be verified in each case. The printed film can be heated under a variety of conditions according to substrate and end-user requirements. SunTronic Jettable Silver is compatible, meaning that it has good adhesion properties, with various substrates such as Kapton, FR4, glass and metals. Compatible flush SunTronic EMD5603 can be used as a head flush with the silver products [5]. The silver ink consists of a solvent (organic or inorganic) together with metallic silver nanoparticles. EMD5603 ink silver content is 20%, but after the thermal treatment the ethanol solvent evaporates and it remains 100% silver [6]. The nanoparticles are typically in the range 1–100 nm. The smallest sizes, i.e. less than 10 nm, have the advantage of lower melting temperatures. The solvent serves as a stabilizing matrix for the nanoparticles and forms protective shells around them to prevent them from coalescence. The solvent is also designed to satisfy the requirements of the printing nozzle. such as drying and viscosity [7]. Usually the sintering temperature is between 50% to 80% of the melting temperature of the material. Usually a furnace is used for sintering, typically at 100–3000C. For this paper the heated temperatures was 130°C for 30 minutes. Silver ink viscosity is between 10 to 13 fps (10-12 fps / 1.0x10-2 - 1.2x10-2 Pa *s specification for printer) and the surface tension is between 27 - 31dynes/cm (2.8-3.3 N / specification for printer), allowing it to be printed [8].

B. Substrate PEN Teonex

The substrate was PEN film Teonex Q65FA with 75 µm thick and the temperature of curing at 130°C. PEN has mechanical properties that are considerably better than competitive products. In particular, PEN substrate shows outstanding performance, with a tensile strength of 520 MPa, and a tensile modulus of 8830 MPa - more than twice of what was previously available. PEN offers excellent elongation of 172% and a tensile strength of 402 MPa. In addition, there is very small degradation of these properties at high temperatures, enabling the use of these materials under extreme temperatures [9].

C. Dielectric PVP

Poly-4-vinylphenol is the dielectric used in this paper. This is due to his properties of special interest, enumerated below: Some of its properties are listed below: PVP powder is white:

- Is stable, hygroscopic and soluble in water. Can react with many substances. In combination with other substances can become brittle and glassy clear visibility [3].

The PEN Teonex Q65FA 75 µm substrate was cleaned first with soap and water, then dried in oven, then cleaned again by wiping and with ethanol. This maintenance is done to remove all traces of particles that could affect the structure.

III. METHODS AND MEASUREMENT

Capacitive structures, as shown in Fig. 2, were printed using a Dimatix DMP 2800 inkjet printer in the clean room. Teonex Q65FA 75 µm, flexible substrate, was used as a support.

Fig. 2. capacitor structure with three layers of silver and two

PVP

For this experiment were using 3 layers of conductor track (silver ink) and two layers for dielectric (PVP). Printing mode is: PEN substrate is printed on the first layer of silver smallest, then the first dielectric layer, followed by a second layer of silver and so on so that PVP dielectric layers are not in contact. PVP layers should cover silver layers, thus forming capacitor. The three layers of silver and two dielectric, structures is the result of two capacitors in series.

The structure was designed in CleWin software.

Fig. 3. Capacitor structure, image software CleWin 4

- Blue, red and pink are the two plates.

- Green and purple is the dielectric PEN substrate cleaned with ethanol by a method known

than that of silver ink printed PVP settings below (Fig. 7.6.1.b.): - Settings first layer of silver substrate temperature of 40oC, the distance between the print head substrate and 125 µm and the distance between drops 20 µm. 4 nozzles were used with voltages of 33V, 34V, 36V and 37V, the speed is 100 mm /Sec and a frequency of 5 kHz printing. After printing silver ink printed structure was subjected to heat treatment in an oven at 130oC for 30 min.

2012 IEEE 18th

International Symposium for Design and Technology in Electronic Packaging (SIITME)

978-1-4673-4760-0/12/$31.00 ©2012 IEEE 79 25-28 Oct 2012, Alba Iulia, Romania

- The first layer of PVP Settings: 40oC substrate temperature, the distance between the print head substrate and 125 µm and the distance between drops 21 µm. They used 5 jets with voltage between 33V-38V; the speed is 105 mm. / Sec and frequency 5 kHz printing. For heat treatment of dielectric substrate PVP setting is 30 min at 100oC for solvent evaporation, 30 min at 150oC for PVP and polymerization time between the two temperatures 15 min. - Settings of the second layer of silver substrate temperature 40oC, the distance between the print head substrate and 125 µm and the distance between drops 20 µm. They used 5 nozzles voltages between 33 V-37 V, speed is 100 mm. / Sec and a frequency of 5 kHz printing. The same heat treatment 130oC for 30 min.

- The second layer of PVP Settings: 40oC substrate temperature, the distance between the print head substrate and 125 µm and the distance between drops 20 µm . 5 nozzles were used with 28V voltage; speed is 105 mm. / Sec and frequency 5 kHz printing. The same heat treatment as the first layer of PVP

- Settings third layer of silver substrate temperature of 40oC, the distance between the print head substrate and 125 µm and the distance between drops 20 µm. We used one nozzle with 28V voltage, speed is 100 mm. / Sec and frequency 5 kHz printing. The same heat treatment 130oC for 30 min.

Table 1 dimension in µm of the printed layers

They followed the same design parameters on the size and structure of each layer heat treatment according to the specifications printed material. In Table 1 are represented the dimensions of the printed layers, according with the Fig. 2, and the final structures is show in Fig.4. The dimension of the PVP is the same. The layers are in this order silver (2490x2480), PVP, silver, PVP and last layer of silver (3640x3570). Measurements were performed, with an Agilent 4396B, to determine the capacity of capacitors and characterize the capacitive structure, as a whole. Some results of the parallel capacity and resistivity are presented in Table 2. Other values can be obtained, but with another structures. Other materials, such as a gold-based ink and a different dielectric surface can increase the load and therefore accumulating capacity will be much higher than that obtained in this work. I have not

measured the tolerance of these structures. Some of these capacitors are not good because of the printer.

Tabel. 2. Measurement results for printed capacitors

Capacitors C1 C2 C3 C4 C5

Capacity Cp /pF 560 326 328 3n 3n

Resistance Rp /MΩ 54 66 56 6.83Ω 6.46Ω

Impedance /Ω 0.27 0.17 0.18 9.98 9.98

Because silver ink containing silver nanoparticles, the print head nozzles may become blocked. Ink remains in the nozzle, which is why printing is not uniform, staying goals conductive material. Print this leads to hollow conductive surface and hence the reinforcement of capacitor failure.

Fig. 5 Capacitor structure, seen in picture printer software Dimatix - view silver layer and PVP.

Regarding the thickness of the tracks, optical and AFM profilometry was employed. KLA Teoner profilometer measurements revealed the irregular thickness of the silver

type

Dimensions (µm)

Silver PVP

3 layer 2 layer 1 layer 1 layer 2 layer

Square

3640x3570 3000x2990 2490x2480 4780x4780

for C 1,2,3

5420x5440 4530x4530 3760x3760 7520x7460

for C 4,5

Fig. 4 Printed capacitor with silver plates and PVP dielectric on

PEN Teonex Q65FA 75 µm substrate

2012 IEEE 18th

International Symposium for Design and Technology in Electronic Packaging (SIITME)

978-1-4673-4760-0/12/$31.00 ©2012 IEEE 80 25-28 Oct 2012, Alba Iulia, Romania

layers and of the PVP layer. The thickness values range as follows:

- For the PVP layer, the value found is 735 µm,, measured in any part of the structure

- For the first layer of silver the thickness was

1.25µm.

IV. CONCLUSION

1. This experiment was intended load accumulation in two capacitors in series. They obtained values of the order of hundreds of pF capacity, which for PVP dielectric are good values. 2. All structures were printed at the same time in the same condiţii.După printing and heat treatment was observed that silver layers are not uniform, resulting in structures that are not capacitors. This is a typical error in printing 3. Using other types of materials (for fittings and dielectric) structures can achieve much higher capacity than those obtained in this work. 4. Printed silver tracks have many satellite drops.

5. Another aspect that was noted is that although the tracks made by ink printing with silver nanoparticles are conductive, they are subject to oxidation and the interconnections should be made immediately to reduce the parasitic resistance

ACKNOWLEDGMENT

The work has been funded by the Sectorial Operational Programme Human Resources Development 2007-2013 of the Romanian Ministry of Labor, Family and Social Protection through the Financial Agreement POSDRU/88/1.5/S/60203.

REFERENCES

[1] Y. Liu, T. Cui, K. Varahramyan, “All-polymer capacitor fabricated with inkjet printing technique”, Solid State Electronics, vol. 47, pp.1543-1548, 2003

[2] Alexander Kamyshny1, Joachim Steinke2 and Shlomo Magdassi1,”Metal-based Inkjet Inks for Printed Electronics” The Open Applied Physics Journal, 4, pp 19-36, 2011

[3] Andreea Brodeala, Andreea Bonea, Ana Alcade, Bogdan Mihailescu, Alexandru Vasile, Paul Svasta “Electrical Characterization of Ink-Jet Printed Organic Capacitors on Flexible Substrate” , ATOM-N 2012 6th edition Advanced Tipics in Optoelectronics, Microelectronics and Nanotechnologies, ISSN 2067-158X, SPIE 8411

[4] Jongwoo Lim a,b, Jihoon Kim, Young Joon Yoon, Hyotae Kim, Ho Gyu Yoon, Sung-nam Lee, Jonghee Kim Republic of Korea “All-inkjet-printed Metal-Insulator-Metal (MIM) capacitor” Contents lists available at ScienceDirect “Current Applied Physics” journal homepage: www.elsevier.com/locate/cap

[5] Technical Information Leaflet PRODUCT Reference SOLSYS

EMD5714, SOLSYS EMD5603 Sun Chemical Corporation.

[6] Technical Information Leaflet PRODUCT Reference SOLSYS EMD5714, SOLSYS EMD5603 Sun Chemical Corporation

[7] Andreea Brodeală, Andreea Bonea, Ciprian Ionescu, Marian Vlădescu, Paul Svasta, “Physical Properties of Silver Inkjet Printed Circuits”, ISSE 2012 35th International Spring Seminar on Electronics Technology „Power Electronics“, ISBN 978-3-85465-015-7, pg 60-62

[8] Technical Information Leaflet PRODUCT Reference SOLSYS EMD5714, SOLSYS EMD5603 Sun Chemical Corporation

[9] Polyimide products, Upilex S, Performance Materials Department, Düsseldorf, Germany.