ABSTRACT Inkjetrinted Radio Frequency Passive Components Inkjet printing is a mature technique for graphic arts. It excels at customized, largearea, highresolution, and smallvolume production. With the developments in conductive, dielectric, and even semiconductinginks theres potential for large area inkjet electronics fabrication. Passive radio frequency devices can benefit greatly from a printing process the size of the devices defined by the frequency of operation. The large size of radio frequency passives mean that they either take up expensive space on chip” or they are fabricated on a separate lower cost substrate and bonded to the chips. This has hindered costsensitive high volume pplications such as radio frequency identification tags. work on inkjetprinted conductors for passive antennas on microwave substrates and even paperlittle work on printing of the dielctric materials aimed at radio frequency passives Both the conductor and dielectric need to be integrated to create a multilayer inkjet printing process capable of making quality passives capacitors and inductors. Three inkjetprinted dielectrics are investigate in this thesisa ceramic (alumina), a thermalcured polymer (poly 4 vinyl phenol), and a UVcure polymer (acrylic based). oth a silver nanoparticle ink a custom in-house formulated particlefree silver ink explored. The focus is mainly capacitors and inductors. ompar to low frequency electronics, radio frequency components have additional sensitivity regarding skin depth of the conductor surface roughness, as well as dielectric constant and loss tangent the dielectric. concerns are investigated with the aim making the highest quality components possible and understand the current limitations of inkjetfabricated radio frequency devices. An inkjetprinted alumina dielectric provides a low loss tangent ~0.001 and high density
ionization energy. This is useful information as the same trends should be seen in an inkjetprinted alumina. Solutionprocessed alumina Recently, solutionprocessed alumina has been demonstrated as a dielectric with good results. This work is not directed towards RF MIMs but driven by thin film transistors, mostly for large area electronics (i.e. displays). Nevertheless, the spincoated films show potential used for RF MIMs and also to be printed. Some notable work in this area is in Table 23. Table 23: Spinoated Alumina Salt & Solvent Bottom & Top Metal (nm) Dk (nm) Leakage (A/cm2) Dk & Df Temp. oC Ref. AlCl3 ACN/EG Mo IZO 110 6.3E-6 4 6.3 - @10KHz 300 Avis 2011 [34] ACN/EG Mo 40 Mo/Au 3/50 120 6.3E-6 1MV/cm 4 7.2 - 300 Kim 2013 [35] AlCl3 ACN/EG p+Si Al 80 95 ~3E-8 @2V - 6.2 - Nayak 2013 [36] AlN3 Acetic Acid Ti-Pt Ti-Pt/Au ~250 10E-7 >1.5 6.5 -7.5 0.01 @1KHz 550 Hu 2013 [37] AlAc 2-ME Mo IZO 70 6.3E-6 4 6.3 - @10KHz 150 Peng 2013 [38]
The spincoated results in Table 23 show the films are not ALD grade but do have low leakage current values and thickness ranges that make it attractive to move towards inkjet printing. Some sol-gel processed semiconductors have similarly moved from spin coating to inkjet, as well as zirconia oxide dielectric [39],[15]. The sol-gel inkjet work demonstrates that creating quality films and printed features challenging. However, it really seems as if it should be attainable. Current inkjetprinted alumina The overall idea is to inkjet print alumina and demonstrate capacitors. A depiction of the process is shown in Figure 21. Figure 21: Inkjet printing of alumina dielectric for MIM capacitors To date, only printed films have been shown with particlebased inks [40], [41]. These provide a rough and thick film 15um, where the use of binders affects the dielectric properties. However, they were able to demonstrate MIM apacitors with Qs of 400 at 1 MHz. Another approach is to use nanoparticles of Al2O3 which has been investigated in [42] although MIM devices were not fabricated. ssues with nozzle clogging from the nanoparticles and difficulties creating thin uniform films with these aqueous solutions appear to be . It is likely that thin nanoparticle films would be inferior to the sol-gel approach due to porosity and grain boundaries. Overall, there have been two demonstrations of inkjet alumina MIM capacitors (low frequency) but non-particle based printing or thinfilm printing of alumina has never been reported to my knowledge. Next, RF MIM capacitors using printed alumina have never een demonstrated for GHz operation. He also used equations for the onset of splashing at Oh = 50/Re5/4 and Oh =2/Re. Figure 35 (c) the operating point (blue dot) where the Dimatix model inkjet fluid fits [72] shows the parameters for the fluid.
Table 31: Dimatix Model Ink Parameters Dimatix Ink Viscosity (cp) Surface Tension Dynes/cm Density g/ml Nozzle Diameter (um) Velocity m/s Re Oh We Ca 10 30 1 21 10 21 0.4 70 3.3