A Novel Switched-Turn Continuously-Tunable Liquid RF MEMS Solenoid Inductor

Transcription

1 A Novel Swithed-Turn Continuously-Tunable Liquid RF MEMS Solenoid Indutor Fatemeh Banitorfian, Farshad Eshghabadi, Asrulnizam Abd Manaf, Norlaili Mohd Noh, Mohd Tafir Mustaffa, Othman Sidek Shool of Eletrial and Eletroni Engineering Universiti Sains Malaysia, Engineering Campus Nibong Tebal, Pulau Pinang, Malaysia Abstrat this paper presents a ontinuously-variable MEMS solenoid indutor operating up to 0 GHz. In this novel idea, a hannel is provided to bypass the turns by injetion of a ondutive liquid (Galinstan). Corresponding to the level of injetion, the redution in number of the turns varies the indutane value. The proposed Solenoid indutor is simulated with HFSS in Silion substrate with Copper-type oil and injeted ondutive liquid. The EM simulation results show a maximum quality fator of 0 at 14 GHz and a tuning ratio of 1:5 at 16 GHz frequeny. The minimum and maximum indutane values are 0.63 and 3.16 nh at 16 GHz whih demonstrates a tuning range equal with 400%. Keywords RF MEMS; tunable indutor; liquid indutor; solenoid; quality fator; tuning range; indutane; liquid-based I. INTRODUCTION The growing market of wireless multi-band systems demands for high-quality highly-linear variable RF MEMS omponents. RF MEMS omponents inluding MEMS indutor have wide range of appliations in RF transeivers suh as VCO [1, ], LNA [3, 4], DC-DC onverters [5-7], mathing networks, multi-band filters, multi-band RF iruits and RF power amplifiers in radio transmitters. MEMS indutors unlike the MMIC indutors benefits from high quality fator whih improve the noise figure in low-noise amplifiers and phase noise in osillators, and also apability for tuning. In the previous works, there are several methods to make indutors tunable by hanging the number of turns [8, 9]. Here, this paper proposes a solenoid indutor whih an ontinuously be tuned. The indutane varies by hanging of the number of the turns in the solenoid indutor while a ondutive liquid flows through the hannel in ontat with the segments of the oil; hene, it bypasses some turns. The main researh issue for integrated tunable passive indutors is high tuning ratio with ontinuous variation state [10]. The hallenge is to ahieve a high quality (>50) indutor with an adequate tuning ratio (>10) operating in a broad frequeny ranges (1-60GHz) until 015 [11]. In [10, 1], indutane variability was proposed based on hanging number of turns in spiral indutor. The novelty in this work whih makes this work new tehnique is injeting ondutive liquid (Galinstan and salted water) between the spiral turns and ause to bypass some of the turns. This work ahieve 107% tuning range in 1.6 GHz frequeny, the peak of quality fator was 1. In [13], tunable indutors based on transformer mutual ation with on-hip miromahined vertial swithes and an atuation gap of a few mirometers was developed. In this work, silver was used as the metal to implement the oil. Six masks were used for fabriation. The indutor an work in 1-10 GHz. The tuning range is alulated as 47% at 6 GHZ with a high Q fator around This paper presents a novel idea to implement a ontinuously tunable RF MEMS solenoid indutor. The tehnique is based on hanging number of turns by injeting a ondutive liquid suh as Galinstan in the hannel whih bypasses the segments. When the ondutive liquid is injeted through the hannel, the liquid start to flow ontinuously and then, it makes the adjaent turns bypassed. The solenoid indutor benefits from silion substrate and opper metal. GaInSn, alled Galinstan is a non-toxi ondutive liquid alloy with eletrial ondutivity of S/m and relative permeability of N.A - [14]. The solenoid indutor proposed in this paper has 40 turns and 0µm 0µm 00µm size. Using the MEMS proess, the hannel is implemented along with the solenoid oil to have the liquid flow inside. The advantage of this work is ontinuously tunability with simple proess for fabriation sine only four mask is required for lithography, and also very high tuning range and adequate quality fator in high frequenies. II. PRINCIPLES FOR TUNABLE MEMS SELONOID INDUCTOR The onept and theory of indutor design inluding indutane and quality fator equations has arisen different tuning tehniques. Equation (1) represents a simplified indutane alulation for a solenoid indutor: 0 r n w t L l 113

2 Fig. 1. 3D simulation in HFSS shows hannel inside the solenoid indutor how onneted to the miropipe, also the pads for measurment is around the indutor. The dieletris are hidden for illustration purpose. where µ 0 and µ r are vauum permeability and relative permeability, respetively; n indiates number of turns and w, t and l represent the width, thikness and length of the oil [15]. Aording to indutane equation, the indutane is diretly proportional with square number of turns; therefore, different values of indutane an be ahieved with hanging number of turns. The tuning method in this paper is based on the idential theory. By injetion of the Galinstan as the ondutive liquid through the hannel whih is implemented to bypass the segments of the oil, the number of turns is allowed to hange from 40 to turns, ontinuously; hene, the indutane varies. Sine the indutane is squarely proportional with number of turns, the tuning range is very high in ompared with the methods using other parameters of indutane equation. The quality fator an simply be found from the ratio of the equivalent reatane and its series resistane: L 0 nw tw t Q R ( w t ) n p r m m where w m, t m, ρ and p are metal width, metal thikness, metal resistivity and turns pith, respetively. As an be observed, number of turns does not have any effet on the quality fator. This means that by hanging of the number of turns, the quality fator maintains onstant; this is true when lossless swithes are used to bypass the turns with zero insertion loss. Here, Galinstan is employed as the ondutive liquid to swithed turns whih its ondutivity is at least ten times lower than the opper. In this ase, we expet more derease in quality fator one more turns are bypassed. Aording to (), it is expeted that quality fator inreases by frequeny inrease, ω. However, the derease of the skin depth with the inrease in frequeny results in redued ondutor ross-setion and inreased resistane, R. The skin effet rises from the eddy urrent; this redues the effetive ross setional area of the segments and hene, inreases the series resistane. Unlike the spiral indutors, the diretion of flux in solenoid-type indutor is parallel with the substrate whih leads to lower substrate loss and skin effet [16]. Beause of this reason, Solenoid indutor indiates higher quality fator than spiral ones. Figure 1 shows a 3D model struture of the proposed indutor. In this figure, the solenoid indutor with a hannel along with the oil is illustrated. Miropipes shown in this figure are onneted to both ends of the hannel for liquid flow from miropipe through the hannel. The miropipes is onneted to the main tank and a miropump pumps the liquid from the tank to the pipe and then, to the hannel. The hannel is loated in ontat with the oil so that the ondutive liquid an ause a short between adjaent turns. III. DESIGN AND FABRICATION Figure illustrates the proess steps for fabriation of the proposed indutor. In this proess, four masks are used. Silion wafer is seleted as the main substrate. The steps are as follow: (a) First, silion oxide film is deposited with phosphorous doping as the sarifiial layer. This auses a distane between the oil and the substrate to improve the quality fator; and then, Au is evaporated as seed layer with 1 µm thikness; (b, ) a positive photoresist is used for opper eletroplating with 3 µm height; (d, e) using a positive photoresist for opper eletroplating, via is reated with 14 µm height. On the top of the via, a seed layer of gold is eletroplated with thikness of 1 114

3 µm without any photoresist. (f, g) The bridge is made by eletroplating opper on the gold with last photoresist mask for 3 µm height; (h) the last step for making the air-bridge is to remove the photoresist with aetone. (i) to make the hannel, SiO is deposited with -µm height, and then (j) PDMS is deposited on the top with 4 µm height. (k) Using fourth mask, the hannel pattern is formed on PDMS for dry ething of SiO. (l) SF6 gas is injeted to remove SiO and to reate an empty hannel; (m) the last step is to over the hannel with PDMS to avoid any liquid leakage for later injetion. Using these steps, the hannel along with the solenoid indutor and in ontat with its segments is reated. Figure 3 shows a prospetive view of steps l. Using a miro pump, the Galinstan is injeted into the hannel and start to flow. A 3D view of the proposed work is given in figure 3 for better understanding. work presents the theory and simulation results. IV. SIMULATION RESULT The indutor is simulated in HFSS one the hannel of the ore is empty (air or vauum) and then, a step-by-step liquid (Galinstan) injetion through the hannel is arried out; in this ase, the variation of the indutane and the quality fator for different levels of injetion is reorded. Figures 4 and 5 shows the plots for the indutane variation and its orresponding quality fator, respetively, for different level of injetions (0% to 100% by step of 11.%). The EM simulation results shows a minimum and maximum indutane value of 0.63 and 3.16 nh in 16 GHz for 0% (empty hannel) and 100% (fully-injeted hannel) levels, respetively. As an be seen in figure 6, the tuning range an be alulated as 400 % in 16 GHz. The maximum quality fator is ahieved by 0 at 14 GHz. As disussed earlier, the quality fator dereases more while more turns are bypassed. This happens beause of lossy ondutive liquid. The worst quality fator happens when the hannel is fully injeted by Galinstan; this forms the longest bypass pattern whih is the most lossy one. In addition; the quality fator inreases with frequeny until a ritial frequeny in whih the skin effet beome effetive in the series resistane and hene, the quality fator. (a) (b) () (d) (e) (h) (i) (j) (k) (l) V. CONCLUSION A novel liquid-based swithed-turn variable indutor was proposed and simulated in HFSS. The variable indutor benefits from a ontinuous tuning state. A tuning range of nH was ahieved at 16 GHz with a maximum quality fator of 0. The advantage of this work is to ahieve high Q fator, wide ontinuous tuning range with simple proess for implementation. The tuning ratio is 5:1 at 16 GHz whih is higher than previous works [1, 13, 17, 18]. This indutor operates in a frequeny range of 3-0 GHz with a Q of over 5 at its worst ase. (f) (g) (m) Fig.. MEMS proess (a) Silion dioxide and gold as seed layer deposition (b) photolithography for eletroplating base mold using first mask, () opper eletroplating, (d) photoresist based on seond mask, (e) opper eletroplating as via, (f) photoresist third mask, (g) opper eletroplating make bridge, (h) remove the photoresist with aetone, (i) deposit SiO, (j) deposit PDMS, (k) fourth mask for make the holes, (l) injet SF6 gas from the holes, (m) hannel beside the solenoid indutor. 115

4 quality fator Q1 0% 11% Q % Q3 33% Q4 44% Q5 56% Q6 67% Q7 78% Q8 89% Q9 100% Q10 Fig. 3. 3D model of fabriation proess shows step (l) with 3D view 0 Fig. 5. EM simulated Quality fator with different levels of Galinstan injeted into the hannel. indutane (nh) L1 0% 11% L % L3 33% L4 44% L5 56% L6 67% L7 78% L8 89% L9 100% L10 Fig. 4. EM simulated Indutane with different levels of Galinstan injeted into the hannel tuning range (%) Fig. 6. Tuning range tuning ratio ACKNOWLEDGMENT Authors would like to thank Collaborative Miro-eletroni Design Exellene Centre (CEDEC) for supporting Coventor software. Also thanks to Universiti Sains Malaysia short term grant no. 1001/PELECT/ Speial aknowledgment to Universiti Sains Malaysia researh university (RU) grant no. 1001/PELECT/ for the funding of this work. REFERENCES [1] P. Eun-Chul, C. Yun-Seok, Y. Jun-Bo, H. Songheol, and Y. Euisik, "Fully integrated low phase-noise VCOs with on-hip MEMS indutors," Mirowave Theory and Tehniques, IEEE Transations on, vol. 51, pp , 003. [] S.-H. Tseng, Y.-J. Hung, Y.-Z. Juang, and M. S.-C. Lu, "A 5.8-GHz VCO with CMOS-ompatible MEMS indutors," Sensors and Atuators A: Physial, vol. 139, pp , 007. [3] H. H. Ali, K. A. Boseli, M. H. Sakr, and M. A. Emara, "A.7v,.4 GHz differential-lna implementation with MEMS tehnology for bluetooth^tm appliations," in Eletrial, Eletroni and Computer Engineering, 004. ICEEC ' International Conferene on, 004, pp [4] H. El Ahmady, A. Zaki, H. Elsimary, and H. Hassan, "Design of Integrated CMOS LNA using Suspended MEMS Indutor for Wireless Appliations." [5] S. Iyengar, T. M. Liakopoulos, and C. H. Ahn, "A DC/DC boost onverter toward fully on-hip integration using new miromahined planar indutors," in Power Eletronis Speialists Conferene, PESC th Annual IEEE, 1999, pp [6] C. H. Ahn and M. G. Allen, "A omparison of two miromahined indutors (bar- and meander-type) for fully integrated boost DC/DC power onverters," Power Eletronis, IEEE Transations on, vol. 11, pp , [7] S. Iyengar, T. M. Liakopoulos, and C. H. Ahn, "A DC/DC boost onverter toward fully on-hip integration using new miromahined planar indutors," in Power Eletronis Speialists Conferene, PESC th Annual IEEE, 1999, pp vol.1. [8] I. Gmati, H. Boussetta, M. A. Kallala, and K. Besbes, "Wide-range RF MEMS variable indutor using miro pump atuator," 008, pp [9] S. Aliouane, A. Kouki, and R. Aigner, "RF-MEMS swithable indutors for tunable bandwidth BAW filters," 010, pp [10] I. El Gmati, P. F. Calmon, A. Boukabahe, P. Pons, R. Fulrand, S. Pinon, et al., "Fabriation and evaluation of an on-hip liquid mirovariable indutor," Journal of Miromehanis and Miroengineering, vol. 1, p , 011. [11] S. Luyszyn, Advaned RF Mems: Cambridge University Press, 010. [1] I. El Gmati, P. Calmon, A. Boukabahe, P. Pons, H. Boussetta, M. Kallala, et al., "Liquid RF MEMS variable indutor," Proedia Engineering, vol. 5, pp , 010. [13] M. Rais-Zadeh, P. A. Kohl, and F. Ayazi, "MEMS swithed tunable indutors," Miroeletromehanial Systems, Journal of, vol. 17, pp ,

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