Liquid Crystal Polymer Substrate Research Articles

Design of Ka Band Patch Microstrip Antenna Array on LCP Substrate

This paper presents a 35 GHz patch microstrip antenna array on an organic LCP (Liquid Crystal Polymer) substrate. To achieve a higher gain and narrower 3 dB beamwidth, a 4×4 antenna array has been designed and simulated using a 2×2 antenna array as unit array. The results show that an 18.9 dBi of gain and a 3 dB beamwidth of 20.7degrees.

Multilayer Inkjet Printing of Millimeter-Wave Proximity-Fed Patch Arrays on Flexible Substrates

Flexible inkjet-printed proximity-fed patch antennas, designed for the 24-GHz Industrial, Scientific, and Medical (ISM) band, are demonstrated in this letter for the first time featuring a multilayer inkjet deposition process. Inkjet printing of antennas allows for the low-cost, noncontact, and additive fabrication of RF components onto nearly any host substrate or package. The inkjet-printing process exhibited in this leter is the first inkjet process to demonstrate multilayer printed antennas, enabled by a new printable dielectric ink that allows for the deposition of thick dielectric layers. Printed coupled patch antennas with realized gains of over 4 dBi and four-element coupled patch arrays with gains of over 7 dBi are demonstrated on a flexible liquid crystal polymer (LCP) substrate. The antenna gain, return loss, and pattern are presented and demonstrate the repeatability and design flexibility of the novel inkjet-deposition process.

A 60-GHz Active Receiving Switched-Beam Antenna Array With Integrated Butler Matrix and GaAs Amplifiers

This paper presents for the first time a 60-GHz receiving switched-beam antenna on organic liquid crystal polymer (LCP) platform. A 4 × 1 quasi-Yagi array is incorporated with a 4 × 4 Butler matrix beamforming network and GaAs low-noise amplifiers on an LCP substrate. The active beam is controlled by GaAs single-pole-double-throw switches to access the four output states of the Butler matrix. The entire 4 × 1 active array is 1.4 cm × 1.75 cm and consumes 1.1 W of dc power. Successful comparisons of the measured and simulated results verify a working phased array with a return loss better than 10 dB across the frequency band of 56.7-63.7 GHz. A comparison of radiation patterns demonstrate beam steering of ±40° with a peak active gain of 27.5 dB. The combined antenna and receiver noise performance at 60 GHz exhibits an estimated merit G/T of -18.6 dB/K and noise figure of 5.4 dB.

Temperature dependence of transmission characteristics of flexible printed circuits in microwave band

The relative complex permittivities of dielectric substrates for flexible printed circuits (FPCs) at 10 GHz were measured by the perturbation method using a cylindrical cavity resonator for temperatures ranging from 27 to 100 °C. The temperature dependencies of the ɛγ and tan δ values of polyimide (PI) substrates were greatly changed by the moisture absorption properties. The ετ and tan δ of a liquid crystal polymer (LCP) substrate were not affected by temperature and were lower than those of the PI substrate below 70 °C. The temperature dependencies of the dielectric losses of microstrip lines (MSLs) for FPCs were evaluated. These losses were found to be more stable and lower for an LCP substrate than for a PI substrate.

Testing of Flexible Metamaterial RF Filters Implemented through Micromachining LCP Substrates

Metamaterials have a wide range of potential uses in areas such as optics, transmission lines, and RF design. The simplest metamaterial structures are Split-Ring Resonators (SRR) and Complementary Split-Ring Resonators (CSSR). Through the combination of various forms of these structures, different applications in the areas previously stated can be achieved. Under this investigation, a metamaterials transmission line was realized through micromachining a Liquid Crystal Polymer (LCP) substrate. Not only does LCP possess useful RF properties, it is flexible and micromachinable. This transmission line consisted of several CSSRs in series, which performed as a high-order, high-frequency filter. This structure was unique to most metamaterial structures because LCP is a flexible substrate. Prototype filters were fabricated and evaluated. One test involved flexing the devices over various radii of PVC pipe sections to evaluate the effects of flexing the substrate on the filter's performance. The filter properties were shown to maintain approximately the same frequency and roll-off while being bent over the various radii of curvature. Therefore, arrays of these filters could be fabricated with planar processes and attached to non-planar surfaces, such as airfoils, for uses such as radar cloaking.

Flexible Dual-Frequency Applicator for Local Hyperthermia

A flexible and dual-frequency microstrip applicator for microwave local hyperthermia is described. It is designed on conformal liquid crystal polymer (LCP) substrate and operating at ISM (Industrial, Scientific and Medical) frequencies of 915 MHz and 2.45 GHz. To conform the body’s curvature, the applicator is bent on a cylindrical body. 3D electromagnetic CST Microwave Studio was used to determine the performance of the applicator and to evaluate the specific absorption rate (SAR) distribution in cylindrical human body phantom. The results obtained show that the antenna can be used in curved situation for uniform and superficial treatment.

Water-resistant flexible GaN LED on a liquid crystal polymer substrate for implantable biomedical applications

A flexible GaN light-emitting diode (LED) has been fabricated on a liquid crystal polymer (LCP) substrate for biomedical applications. The bending radius and fatigue tests demonstrated the mechanically and optically stable characteristics of the GaN LEDs on the flexible substrates. A white light-emitting phosphor-coated GaN LED showed its potential as a next-generation flexible light source. A water-resistant and biocompatible polytetrafluoroethylene (PTFE) coated flexible LED detected prostate-specific antigen (PSA), which is expected to be used in future biomedical devices.

Integration of thin film bulk acoustic resonators onto flexible liquid crystal polymer substrates

Thin film bulk acoustic resonators (FBARs) have been directly integrated on liquid crystal polymer (LCP) substrates for application to the field of flexible electronics. Particular developments required were chemo-mechanical polishing for LCP roughness reduction to enable growth of high quality ZnO films and a through substrate deep reactive ion etch process. Q values of up to 126 and 78 for series and parallel resonances combined with an electromechanical coefficient ( k t 2 ) ∼ 6.7% were achieved. Further device development is needed but this performance is already sufficient for some chemical/biological sensing applications.

Flexible Metamaterials RF Filters Implemented through Micromachining LCP Substrates

Metamaterials have a wide range of potential uses in areas such as optics, transmission lines, and RF design. The simplest metamaterial structures are Split-Ring Resonators (SRR) and Complementary Split-Ring Resonators (CSSR). Through the combination of various forms of these structures, different applications in the areas previously stated can be achieved. Under this investigation, a metamaterials transmission line was realized through micromachining a Liquid Crystal Polymer (LCP) substrate. Not only does LCP possess useful RF properties, it can also be easily micromachined. This transmission line consisted of several CSSRs in series, which performed as a high-order, high-frequency high-pass filter. This structure was unique to most metamaterial structures because LCP is a flexible substrate. It was observed that the resonant frequency of the filter did not change when the LCP transmission line was flexed in various ways. Next, micromachined vias were etched through the LCP substrate to demonstrate that these features do not affect the filter's response. Through utilization of these vias, the metamaterial structures can be physically conformed to nearly any shape or mounted onto another object without affecting the filter's response. As demonstrated in a simple filter structure, the shape manipulation has very little effect. Theoretically, extrapolating these methods to the development of metamaterials 3D RF invisibility cloaks, that are easily realizable and mountable onto an object, could prove useful.

Multilayer Integration of Low-Cost 60-GHz Front-End Transceiver on Organic LCP

This letter presents a low-cost and lightweight transceiver with RF front-end components integrated on multilayer organic liquid crystal polymer (LCP) substrate for 60-GHz wireless communication applications. Two embedded dual-mode filters with an insertion loss of 3.1 and 2.4 dB are included, while they are designed to improve the isolation between the transmitting and receiving modes. A package-integrated high-gain vertical dipole is used for the radiating element with orthogonal polarization between the transmitting and receiving modes. The transceiver module after integrating a power amplifier (PA) and a low noise amplifier (LNA) for each mode has a measured gain of 12 dBi for the transmitting mode at 61.5 GHz and 22 dBi for the receiving mode at 66 GHz.

High Efficiency Wideband Aperture-Coupled Stacked Patch Antennas Assembled Using Millimeter Thick Micromachined Polymer Structures

Micromachined stacked patch antenna devices with high efficiency and wideband characteristics are reported. Polymer based fabrication and assembly processes have been developed in order to produce the stacked suspended antenna devices. Millimeter thick micromachined SU8 based polymer rings are used to create air gaps between the patches and the microwave substrate for optimized high efficiency operation. Thin film liquid crystal polymer (LCP) and polyimide substrates are used to support the radiating and parasitic patch elements. The polymer rings also form cavities to protect the patches and substrate from moisture and dust. The antenna structures are fabricated in layers and then assembled to obtain 3D devices. The antenna devices have been designed using an electromagnetic simulation package. The aperture coupled devices are impedance matched for wideband operation. RF measurements show wideband operation of the devices and the results are in good agreement with that of simulation. Typical gain and bandwidths are 7.8 dBi and 39% for a microstrip fed antenna device while they are 7.6 dBi and 44% for a CPW fed device. The predicted efficiency from the results of simulation is above 97% for the antenna devices.

Flexible antenna based on composite right/left-handed transmission line

A flexible antenna based on the composite right/left-handed transmission line is proposed. The flexible antenna is fabricated on liquid crystal polymer substrate with a thickness of 80 µm. The antenna operates at 2.3 GHz and its size is 38×43 mm. The return losses of the proposed antenna are almost unchanged while it is bent from −90° to +90°.

A miniature rigid/flex salinity measurement device fabricated using printed circuit processing techniques

The design, fabrication and initial performance of a single substrate, miniature, low-cost conductivity, temperature, depth (CTD) sensor board with interconnects are presented. In combination these sensors measure ocean salinity. The miniature CTD device board was designed and fabricated as the main component of a 50 mm × 25 mm × 25 mm animal-attached biologger. The board was fabricated using printed circuit processes and consists of two distinct regions on a continuous single liquid crystal polymer substrate: an 18 mm × 28 mm rigid multi-metal sensor section and a 72 mm long flexible interconnect section. The 95% confidence intervals for the conductivity, temperature and pressure sensors were demonstrated to be ±0.083 mS cm−1, 0.01 °C, and ±0.135 dbar, respectively.

Back-to-back tunable ferroelectric resonator filters on flexible organic substrates.

This paper presents the design and the fabrication of two low-loss X-band back-to-back tunable ferroelectric resonator filters on flexible liquid crystal polymer substrates using wire-bonded BST capacitors as analog tuning elements. The back-to-back topology consists of three resonators on both sides of the substrate coupled by apertures in their common ground plane, allowing the overall size of the filter to be reduced. BST varactors made on a sapphire substrate are easily diced and mounted on the polymer substrates to achieve the desired tuning. Both 3-pole tunable filters show a 1-dB bandwidth of 8 to 10%, low insertion loss (3.6 to 1.95 dB for the best one) with bias voltages from 0 to 35 V, a better compactness compared with classical tunable structures (reduced footprint area by 30% for the best filter) and a frequency tuning of about 11 to 13% at 8 GHz. The demonstrated feasibility opens interesting prospects for the fabrication of compact tunable filters with more resonators.

Back-to-back tunable ferroelectric resonator filters on flexible organic substrates

This paper presents the design and the fabrication of two low-loss X-band back-to-back tunable ferroelectric resonator filters on flexible liquid crystal polymer substrates using wire-bonded BST capacitors as analog tuning elements. The back-to-back topology consists of three resonators on both sides of the substrate coupled by apertures in their common ground plane, allowing the overall size of the filter to be reduced. BST varactors made on a sapphire substrate are easily diced and mounted on the polymer substrates to achieve the desired tuning. Both 3-pole tunable filters show a 1-dB bandwidth of 8 to 10%, low insertion loss (3.6 to 1.95 dB for the best one) with bias voltages from 0 to 35 V, a better compactness compared with classical tunable structures (reduced footprint area by 30% for the best filter) and a frequency tuning of about 11 to 13% at 8 GHz. The demonstrated feasibility opens interesting prospects for the fabrication of compact tunable filters with more resonators.

71–86 GHz antenna–MMIC interface using stacked patch configuration

A stacked patch configuration is used to electromagnetically couple a GaAs MMIC chip to a patch antenna integrated in the lid of the MMIC package. The lid is formed using a liquid crystal polymer substrate. Presented is the first implementation that covers the E-band frequency range from 71–86 GHz for long-range wireless communications. Antenna gain is greater than 8 dBi using a short horn with straight sidewalls.

Reduced-size multilayer X-band filters with stacked resonators on a flexible organic substrate

This work presents the design of two four-pole, quasi-elliptic microwave bandpass filters with stacked open-loop resonators on an emerging low-loss organic dielectric material. Both filters are based on a multilayer microstrip structure that uses low-cost and flexible liquid crystal polymer substrates to produce a compact size. The first filter, which has a bandwidth of 17% at 9.3 GHz, was designed to control the high coupling strength between overlapped resonators without sacrificing its compact size. It has a measured 1.7 dB of insertion loss. The second filter uses the same topology, but its measured parameters include a bandwidth of 9% at 10.5 GHz and an insertion loss of 4.5 dB. To achieve the 9% bandwidth, two metallic patches were added between layers to limit the higher coupling between the overlapped resonators. Both bandpass filters have a footprint area reduction of at least 25% when compared to an equivalent single-layer, open-loop resonator filter.

Analysis of Adhesion and Fracture Energy of Nano-Particle Silver in Electronics Packaging Applications

Nano-particle silver (NPS) conductors are increasingly being investigated for package level electronics applications. Unlike traditional thick film materials and conductive inks, nano-particle conductors often do not incorporate compounds to promote interfacial adhesion such as binders used in thick films and polymer adhesives used in conductive inks as these adhesion promoters can degrade the electrical performance. The NPS is concerned with low adhesion to most of processed polymer surface such as liquid crystal polymer (LCP), polyimide, and benzocyclobutene (BCB). Moreover, the adhesion mechanism of NPS has not been identified yet. Thus, as a first step to identify NPS adhesion mechanism and thus, to improve NPS adhesion, quantitative measurement of the adhesion strength of NPS is necessary. Since conventional adhesion test methods are not directly applicable to thin (~ 2 ¿m) NPS film adhesion test, a new adhesion test method is developed in this paper to estimate the adhesion strength of NPS films. The newly developed adhesion test method is called modified button shear test (MBST) because it modifies the conventional button shear test and integrates the generally known die shear test. The MBST is used for measuring not only interfacial bond strength, but also interfacial fracture energy. The interfacial bond strength in tension and the interfacial fracture energy of NPS with LCP substrate measured by MBST are 24.4 MPa and 17.2 J/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. The MBST is generic in nature and can be extended to other thin films adhesion test for measuring interfacial bond strength and interfacial fracture energy.

Understanding Cleaning of Vias Fabricated Using Micro Mechanical Punching in Liquid Crystal Polymer (LCP) Substrate

The objective of the research is to understand the effect of chemical treatment's etching times on via wall roughness; and the direct current (DC) and reverse pulse plating (RPP) of vias fabricated using micro mechanical punching process on liquid crystal polymer (LCP) substrate. One major drawback of micro mechanical punching process is the formation of LCP and copper burrs. Sequential wet chemical etching and oxygen plasma cleaning techniques were developed as an effective tool for the removal of these burrs. The wet chemical process required a sequential oxidation, etching, and acid neutralization treatment for the effective removal of LCP and copper burrs. These treatments have an effect on the surface roughness of the through via wall. Under this research time dependent experimental matrices were designed to observe the effect of the wet chemical etching on the via wall surface roughness. Sequential oxidation, etching, and acid neutralization treatments were done, where only one treatment time was varied for 1, 5, and 10 minutes keeping the other treatment times constant at 5 minutes. After examining three different experimental matrices for via wall roughness using a scanning electron microscope (SEM), it was observed that the longer treatment time using chemical etchant will make the surface rougher. In addition, it was also observed that the oxidation treatment time of greater than 5 minutes produced the same roughness irrespective of treatment time variation. The neutralization treatment time does not have any effect on the roughness of the LCP via wall. Two different approaches named - DC and reverse pulse plating (RPP) were used to plate the vias. It was found that the RPP does not result in good via filling, because it produced high current concentration at the edges and consequently over plating at the edge compared to the inside of the via. In stark contrast, DC plating delivers completely plated vias after 4.5 hours, which is a 7 μm/hr plating rate.

Cu based patch antenna on polymer substrate for flexible wireless sensor systems applications

In this work we designed, simulated and developed a flexible 10 GHz patch antenna using standard microsystem technology. Liquid crystal polymer (LCP) is used as substrate and Copper (Cu) as metallization thin film. LCP and Cu are best suited for high frequency applications because of their excellent electrical properties such as resistivity and dielectric constant. To protect the antenna it is passivated and encapsulated with parylene C. Parylene C was deposited at room temperature using standard Gorham system. The effect of Cu metallization and parylene C passivation on antenna indicator parameters such as resonance frequency, input reflection coefficient, bandwidth and gain are investigated. Furthermore the specific resistance of Cu lines on LCP substrates is investigated.