Li2ZnTi3O8 based High κ LTCC tapes for improved thermal management in hybrid circuit applications

doi:10.1016/j.ceramint.2017.01.073

Ceramics International

Volume 43, Issue 7, May 2017, Pages 5509-5516

https://doi.org/10.1016/j.ceramint.2017.01.073 Get rights and content

Abstract

A low temperature co-fired ceramic based on Li₂ZnTi₃O₈ (LZT), that possess auspicious thermal and dielectric properties is reported. In order to achieve the low sintering temperature suitable for LTCC applications (875 °C), 1 wt% of 20:Li₂O-20: MgO-20: ZnO-20:B₂O₃-20: SiO₂ (LMZBS) glass was added to LZT ceramics. The post-milled powder had an average particle size of 450 nm with an effective surface area of 0.812 m²g⁻¹. A well dispersed tape casting slurry was prepared using xylene/ethanol mixture as solvent and fish oil as dispersant. The crystal structure and microstructure of the tapes were analyzed through XRD and scanning electron microscopy (SEM). The microwave dielectric properties of the green as well as sintered tapes were measured at different frequencies (5, 10 and 15 GHz). The Li₂ZnTi₃O₈+1 wt% LMZBS has shown excellent thermal conductivity of 5.8 W/mK, thermal expansivity (11.97 ppm/°C) closer to silver electrode, low temperature coefficient of dielectric constant (−29 ppm/°C) and ultralow dielectric losses (tanδ~10⁻⁴).

Introduction

The size reduction trend of hand held electronic devices have now grown into newer dimensions with the advent of hybrid circuit concept, which is realized by embedding passive components at the intermediate layers, giving ample room to mount active components on the surface of the multilayer structure. In this direction, low temperature co-fired ceramic (LTCC) technology has attracted much attention because of its ease of design and functional benefits due to excellent electrical performance, partly contributed by enabling highly conductive electrode metals like Ag, Cu, Au etc [1], [2], [3]. For an ideal material to be qualified for LTCC applications, besides lower sintering temperature (<950 °C), it should possess low dielectric constant (ε_r<10), low dielectric loss (tanδ<10⁻³), tolerable coefficient of thermal expansivity (CTE) with respect to electrodes (<20 ppm/°C) and high thermal conductivity (>10 W/mK). Surprisingly enough, most of the commercial LTCC substrate possesses CTE close to silicon (<5 ppm/°C), which can exert thermal stress on passive components due to the former's higher thermal expansivities (>15 ppm/°C). Secondly, achieving high thermal conductivity is also harder to realize, since most of the ceramics have lower thermal conductivities, which gets further lowered with the addition of glasses. Nonetheless, any material that qualifies to show a thermal conductivity above 5 W/mK is really appreciable since they can partly eliminate thermal vias in certain specific LTCC applications.

Lowering the sintering temperature without deteriorating the dielectric properties is the principal hurdle towards the goal of developing a successful LTCC material. In general, plenty of techniques are available to lower the sintering temperature of ceramic materials such as addition of glasses and low melting oxides as sintering aids, chemical processing, using smaller particles as the starting materials and so for [4]. Recent works suggest that, the use of a proper low loss and low temperature melting glass as a sintering aid, is the most suitable approach in this direction [5], [6]. It was reported that multicomponent glasses are more effective than single component glasses in the aspect of possessing better dielectric properties. The selection of a suitable sintering aids is of prime importance, because in some cases the addition of an improper glass may deteriorate the microwave dielectric properties besides aggravating the grain growth, which permits some ions from glassy phase to substitute at the matrix lattice and form satellite phases [7].

Commercial LTCC materials in general, are found to possess low dielectric constants (ε_r<10), which pose little freedom to microelectronic circuit designers. However, certain specific applications such as microwave filters demand high dielectric constant LTCC tapes as substrates in hybrid circuits. It should be noted that non ferroelectric, high dielectric constant, but low loss LTCC substrates are advantageous since they have smaller levels of cross talk. Interestingly, there is a surprising scarcity of literature on high dielectric constant LTCC materials except a few studies like Zhou et al. who developed a Bi₂Mo₂O₉ based LTCC material with high dielectric constant [8]. Recently a few high dielectric constant compositions of ultra-low temperature co-fired ceramics (ULTCC) based on (1−x)BiVO₄-xTiO₂ (x=0.4, 0.50, 0.55 and 0.60) were also reported [9]. Other than these isolated research and development reports, LTCC tapes with high dielectric constant (ε_r>20) are not at all available in the commercial market. The present paper is a candid attempt in this direction to develop a novel LTCC substrate possessing ε_r>21 in the sintered form, along with a combination of low dielectric loss and interesting thermal and mechanical characteristics. This kind of LTCC materials can also serve as a buffer layer between piezoelectric laminates (a passive component) and low loss dielectric laminates (a signal processing component), in periodic multilayer structures.

Recently, a resurged interest was generated on the spinel structured Li₂ZnTi₃O₈ based ceramic system because of their comparatively low sintering temperature (1075 °C) and excellent dielectric properties [10], [11], [12]. Blasse et al. in 1963 reported Li₂ZnTi₃O₈ for the first time. Later, its stoichiometry and crystal structure have been investigated by Hernandez et al. [9], [12] In 2010 Sumesh et al. reported the microwave dielectric properties of Li₂ZnTi₃O₈ sintered at 1075 °C for the first time (ε_r=25.6, Q_uxf=72000 GHz and τ_f=−11.2 ppm/°C) [12]. Huang et al. investigated the effect of Mg and Co doping on the microwave dielectric properties of Li₂ZnTi₃O_8. They obtained high Q factor for the compositions Li₂(Zn_0.94Mg_0.06)Ti₃O₈ (Q_uxf=150000 GHz) and Li₂(Zn_0.92Co_0.08)Ti₃O₈ (Q_uxf=140000 GHz) [13]. Subsequently, a lot of research work was carried out on different LTCC compositions involving Li₂ZnTi₃O₈ [14], [15]. Recently, Sumesh and Sebastian reported the microwave dielectric properties of Li₂ZnTi₃O₈+1 wt% LMZBS glass composite [16]. The bulk ceramic composite sintered at 925 °C has a dielectric constant of 24.3, Q_uxf=58000 GHz with a τ_f of −11 ppm/°C. Besides, the said composite is chemically compatible with silver electrode material. In the present study, we have employed a non aqueous based tape casting technique, in order to develop Li₂ZnTi₃O₈+1 wt% LMZBS (LZT+LMZBS) glass composite as a candidate material for high κ LTCC applications. The structural, microstructural, thermal, dielectric and mechanical properties of the newly developed LTCC tape sintered at 875 °C were analyzed. In comparison with the commercial LTCC products, the new LTCC material has a higher coefficient of linear expansivity (CTE) and thermal conductivity, that can complement to enhance their reliability.

Section snippets

Preparation of LZT+LMZBS glass composite

Li₂ZnTi₃O₈ (LZT) was synthesized by solid state ceramic route using high purity Li₂CO₃ (99%), ZnO (99.9%), and TiO₂ (99.8%) from Aldrich (St. Louis. MO, USA) as the starting materials. Stoichiometric amounts of all these chemicals were ball milled together in ethanol medium using yttria stabilized zirconia balls for 24 h. The slurry was then dried overnight in a hot air oven at a temperature of 100 °C and was calcined at a temperature of 900 °C in a high temperature furnace with a dwell time of 4

Properties of LZT+LMZBS glass ceramic

Lithium zinc titanate belongs to the spinal family having AB₂O₄ structure, where A and B refers to the cations in the tetrahedral and octahedral positions respectively. Two different structure configurations are possible for a spinal, namely A(B₂)O₄ distribution and the inverse spinel, B(AB)O₄, where the parenthesis represents octahedral site position. The system Li₂O–ZnO–TiO_2, crystallizes in cubic spinel crystal structure with space group P4₃32. Fig. 1(a) shows the XRD pattern of LZT+LMZBS

Conclusion

LZT+LMZBS prepared by solid state ceramic route was used as the filler for the preparation of LTCC tape casting slurry. Rheological studies reveal that in the first stage of the slurry preparation 1.5 wt% fish oil is optimum amount as a dispersant, with respect to the ceramic powder. This will get modified to 0.71 wt% with respect to the total weight of the slurry, when suitable amounts of plasticizers, binder and homogenizer were added in the second stage. Uniform and homogeneous slurry was tape

Acknowledgements

Authors are grateful for the financial support from the DST funded project (File no: DST/TSG/NTS/2012/89). The authors are also thankful to Dr. P. Prabhakar Rao and Mr. M. R. Chandran for extending SEM and XRD, Dr. Yoosaf Karuvath and Mr. Aswin for the AFM, and Mr. A. Peer Mohamed for TG and BET facilities.

References (45)

H. Naghib-Zadeh et al.
Low temperature sintering of barium titanate based ceramics with high dielectric constant for LTCC applications
J. Eur. Ceram. Soc.
(2011)
X. Lu et al.
Microwave dielectric properties of Li₂ZnTi₃O₈ ceramics doped with Bi₂O₃
Ceram. Int.
(2013)
R. Tickoo et al.
Microindentation studies on samarium-modified lead titanate ceramics
Mater. Chem. Phys.
(2003)
O. Dernovsek et al.
LTCC glass-ceramic composites for microwave application
J. Eur. Ceram. Soc.
(2001)
I.J. Induja et al.
LTCC tapes based on Al₂O₃–BBSZ glass with improved thermal conductivity
Ceram. Int.
(2015)
D. Hotza et al.
Review: aqueous tape casting of ceramic powders
Mater. Sci. Eng. A.
(1995)
D. Thomas et al.
Casting and characterization of LiMgPO₄ glass free LTCC tape for microwave applications
J. Eur. Ceram. Soc.
(2013)
C.A. Gutiérrez et al.
Tape casting of non-aqueous silicon nitride slips
J. Eur. Ceram. Soc.
(2000)
L. Palmqvist et al.
Dispersion mechanisms in aqueous alumina suspensions at high solids loadings
Colloid Surf. A
(2006)
S. Li et al.
Fabrication and characterization of Li_1+x−yNb_1−x−3yTi_x+4yO₃ substrates using aqueous tape casting process
Ceram. Int
(2009)

L.A. Salam et al.

Optimisation of thermoelectric green tape characteristics made by the tape casting method

Mater. Chem. Phys.

(2000)

L.A. Salam et al.

Pyrolysis of Polyvinyl Butyral (PVB) Binder in Thermoelectric Green Tapes

J. Eur. Ceram. Soc.

(2000)

P. Abhilash et al.

Glass free, non-aqueous LTCC tapes of Bi₄(SiO₄)₃ with high solid loading

J. Eur. Ceram. Soc.

(2015)

J.J. Bian et al.

Designing of glass-free LTCC microwave ceramic- Ca_1−x(Li _0.5Nd_0.5)_xWO₄ by crystal chemistry

J. Am. Ceram. Soc.

(2012)

J. Guo et al.

Synthesis, structure, and characterization of new low-firing microwave dielectric ceramics: (ca_1−3xBi_2xΦ_x)MoO₄

J. Mater. Chem. C.

(2014)

M.T. Sebastian et al.

Low loss dielectric materials for LTCC applications: a review

Int. Mater. Rev.

(2008)

L. Fang et al.

Novel low-firing microwave dielectric ceramic LiCa₃MgV₃O₁₂ with low dielectric loss

J. Am. Ceram. Soc.

(2013)

T. Joseph et al.

Tape casting and dielectric properties of Sr₂ZnSi₂O₇-based ceramic-glass composite for low-temperature co-fired ceramics applications

Int. J. Appl. Ceram. Technol.

(2011)

P.S. Anjana et al.

Microwave dielectric properties and low-temperature sintering of cerium oxide for LTCC applications

J. Am. Ceram. Soc.

(2009)

D. Zhou et al.

Dielectric properties of an ultra-low-temperature cofiring Bi₂Mo₂O₉ multilayer

J. Am. Ceram. Soc.

(2010)

D. Zhou et al.

Novel temperature stable high-ε_r microwave dielectrics in The Bi₂O₃ –TiO₂ –V₂O₅ system

J. Mater. Chem. C.

(2016)

G. Blasse

The structure of some new mixed metal oxides containing lithium

J. Inorg. Nucl. Chem.

(1963)

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Li2ZnTi3O8 based High κ LTCC tapes for improved thermal management in hybrid circuit applications

Abstract

Introduction

Section snippets

Preparation of LZT+LMZBS glass composite

Properties of LZT+LMZBS glass ceramic

Conclusion

Acknowledgements

J. Eur. Ceram. Soc.

Ceram. Int.

Mater. Chem. Phys.

J. Eur. Ceram. Soc.

Ceram. Int.

Mater. Sci. Eng. A.

J. Eur. Ceram. Soc.

J. Eur. Ceram. Soc.

Colloid Surf. A

Ceram. Int

Mater. Chem. Phys.

J. Eur. Ceram. Soc.

J. Eur. Ceram. Soc.

Designing of glass-free LTCC microwave ceramic- Ca1−x(Li 0.5Nd0.5)xWO4 by crystal chemistry

J. Am. Ceram. Soc.

Synthesis, structure, and characterization of new low-firing microwave dielectric ceramics: (ca1−3xBi2xΦx)MoO4

J. Mater. Chem. C.

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Novel low-firing microwave dielectric ceramic LiCa3MgV3O12 with low dielectric loss

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