Design and evaluation of PZT thin-film micro-actuator for hard disk drives

Sensors and Actuators A 116 (2004) 329–335

Design and evaluation of PZT thin-film micro-actuator for hard disk drives Yang Jing a,∗ , Jianbin Luo a , Xiaoxing Yi b , Xin Gu a a

State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, PR China b Institute of Acoustics, Chinese Academy of Sciences, Beijing 100080, PR China

Received 14 November 2003; received in revised form 14 April 2004; accepted 3 May 2004 Available online 10 June 2004

Abstract A new thin-film PZT micro-actuator bonded to a stainless steel (SUS304) suspension for positioning a magnetic head for high-density hard disk devices has been designed, fabricated and investigated. This PZT micro-actuator in dual-stage serve system was made using a sol–gel technique deposited thin-film PZT and applying reactive ion etching processes to fabricate the micro-actuator. The SUS304 cantilever beam integrated with the PZT micro-actuator was also simulated in order to test the driving mechanics. The novel piezoelectric multi-layer micro-actuators possess a useful compromise performance in displacement, resonance frequency and generative force. The results reveal that the new design concept provides a valuable alternative for multi-layer piezoelectric actuators. When a double-layer thin-film PZT micro-actuator was used, an applied voltage of ±15 V was sufficient to obtain 0.9866 ␮m tip displacement of the cantilever beam and high-resonance frequency over 16.67 kHz, yielding the required servo bandwidth (13 kHz) of several kHz. © 2004 Elsevier B.V. All rights reserved. Keywords: Dual-stage serve system; Hard disk drives; Micro-actuator; PZT; Piezoelectric thin film

1. Introduction The main magnetic data storage device in a computer system is the hard disk drive (HDD) [1,2]. In HDDs, data are stored on concentric data tracks on rotating disks and are read by a radially traversing, mechanically positioned magnetic head. During the past several years, the recording density and spindle rotation speed of HDDs continues to advance at a remarkable rate. Now, bite density (BPI) has been increasing significantly by using advanced head and media technology, whereas the track density (TPI) still remains at a relatively low level [3]. To attain higher track densities, extremely accurate track following is required. It is generally accepted that, in order to maintain this growth rate, some fundamental configurations may have to change [4–6]. In the past 8 years, the use of dual-stage actuator system (DSA) in HDDs has attracted significant attention and has been deemed to be one of the most promising technologies to achieve higher data track densities. A dual-stage actuator system comprises a conventional

∗ Corresponding author. Tel.: +86-1062771438; fax: +86-1062771379. E-mail address: [email protected] (Y. Jing).

0924-4247/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2004.05.006

voice coil motor (VCM) as the primary actuator for track seeking, coupled with a second micro-actuator for settling and track following [7,8]. And the key idea of constructing a dual-stage servomechanism is to mount a small piggyback actuator as shown in Fig. 1, capable of positioning the magnetic head with great accuracy and speed, on a VCM. The structure, performance and mounting location of the secondary actuator are key factors affecting the overall characteristic of the dual-stage servo systems. Taking the inertia of the entire actuator mechanism into consideration, the mounting place of the secondary stage actuator should be as close to the magnetic head as possible [9–11]. On the other hand, the driving electric/magnetic field of the actuator should not affect the read/write performance of the magnetic head. From this point of view, the optimum location of the secondary micro-actuator will be backside of the slider. It has already been reported that the piezoelectric property of thin-film PZT is superior and it is applied to various electronic devices such as pyroelectric sensors, acceleration sensor, etc. It is also expected to apply to various actuator devices [13]. In our research, a PZT (lead-zirconate titanate) thin-film micro-actuator that is longer and wider than its thickness is presented. Furthermore, in order to apply the thin-film PZT to the actuator devices, in this study, we

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coating. By applying alternating voltage with opposite phase to each other to the two PZT elements, the head slider rotates around the dimple pivot on the suspension. 2.2. Micro-actuator fabrication process

Fig. 1. Improved piggyback micro-actuator HGA consists of slider, suspension and PZT thin films.

have developed a novel manufacturing process of sol–gel thin-film PZT actuator for HDDs, in which the thin-film PZT is made free from the stress by removing the mostly silicon substrate and is then glued to a stainless steel (SUS304) substrate. The deposition process and structure of these PZT films will be presented. In addition, we investigated the piezoelectric coefficient d31 by cantilever deflection measurements using a finite element method (FEM).

2. Design and evaluation of PZT micro-actuator

The field of micro-electromechanical systems (MEMS) is growing rapidly [14–16]. Micro-mechanical structures are currently being investigated for a wide variety of applications because they are generally several orders of magnitude smaller than their conventional counterparts and can easily be integrated with electronic circuits. Moreover, current reactive ion etching (RIE) processes are able to achieve high aspect ratio (>25:1) silicon (Si) mechanical structures, which can hardly be achieved by conventional machining techniques [17,18]. These high precision fabrication techniques present the possibilities of achieving high performance and multiple functionalities in mechanical structures, with low fabrication cost. Thus, MEMS is considered to be among the most promising technique, to keep up or even accelerate the miniaturization trend in the HDD industry. Fig. 2 shows a photograph of the thin-film PZT micro-actuator element developed for a DSA device for HDDs. Furthermore, Fig. 3 shows a cross-sectional view of the micro-actuator structure. A thin PZT double-layer coating was deposited on a silicon plate as the active material and bonded to a SUS304 substrate. Each of the layers was polarized inward, and the layers are polarized opposite to the flexure of the SUS304 substrate. Each PZT monolayer is coated with Pt electrodes on both surfaces, with applied voltage of −15 V on the inner electrode of the double-layer and +15 V on the top and bottom electrodes. At the beginning of the fabrication process, on an oxidized (1 0 0)-orientation silicon wafer, the bottom electrode was sputtered which consists of a 20 nm titanium layer and a

2.1. Micro-actuator structure Fig. 1(a) shows the design of the thin-film PZT micro-actuator developed for a dual-stage actuator device for HDDs. The micro-actuator is composed of double-layer PZT films bonded to both sides of a rectangular stainless steel (SUS304) substrate. Typical values for the film properties and dimensions are listed in Table 1. Fig. 1(b) shows the structure illustration of the PZT micro-actuator that consists of slider and PZT multi-layer Table 1 PZT multi-layer thin film properties and dimensions Parameter d31 (m/V) [12]

Value

−50 e−12

PZT monolayer sizes

Electrode thickness (␮m)

Thickness, t (␮m)

Length, l (mm)

Width, w (mm)

Pt

Ti

0.6

1.2

0.6

0.1

0.01

Fig. 2. The thin-film PZT micro-actuator element.

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331

Fig. 4. XRD pattern of the PZT micro-actuator element. Fig. 3. Cross-sectional view of the PZT micro-actuator.

120 nm Pt layer. The deposition technique of the bottom electrode was optimized to achieve 1 1 1-orientation [19]. A 600 nm PZT thin film with a Zr/Ti ratio of 58/42 was deposited by a modified sol–gel technique to yield a high piezoelectric coefficient. In step 2 a Ti/Pt/Ti electrode layer was RF-sputtered which consists of two 10 nm thick titanium layers and a 100 nm thick Pt layer and structured using a reactive ion etching process. In a similar way, a sol–gel PZT layer and a Pt/Ti top electrode were deposited on these layers and structured using the RIE process, respectively. Afterwards, the contact pads (Al) and an encapsulation layer (SiO2 ) was deposited and structured using a lift-off process. The bulk silicon was removed from the backside of the Si substrate in a wet etching process and leave only 20 ␮m thickness Si substrate. In a last step, two PZT multi-layer coatings with 20 ␮m Si substrate were bonded to both sides of a 50 ␮m thick SUS304 cantilever using an epoxy resin (it is need 15 min in 120 ◦ C to cure it). The PZT thin films were formed by sol–gel deposition process. Before deposition, a PZT precursor solution is prepared by dissolving proper quantities of lead acetate [Pb(CH3 COO)2 ·3H2 O], zirconium nitrate [Zr(NO3 )4 ·5H2 O] and tetra butyl titanate [Ti(OC4 H9 )4 ] in a 2-methoxy ethanol to form a PZT solution. Then, the solution was spin-coated in several layers on the wafer. Each layer was pyrolyzed using a hot plate. To reach a total thickness of 600 nm of PZT monolayer eight coating cycles were carried out. After deposition, the resulting multi-layer PZT thin films are subjected to an annealing process to obtain a well-crystallized thin film. The annealing process is carried out at a temperature of about 650–750 ◦ C for a duration of about 30–45 min. The manufacturing process of the present paper is unique from the following points of view: (1) Displacement per applied voltage can be made large by the double-layer PZT structure. (2) Piezoelectric coefficient (d31 ) can be maximized by removing the mostly Si substrate and freed from stresses. Also, the glued films on SUS304 cantilever are bending free.

Fig. 5. Diagram of the simple SUS304 cantilever beam with PZT actuator.

The phase content of the micro-actuator element was identified by X-ray diffraction (XRD) using a D/max-RB diffractometer with a monochromated high intensity Cu K␣1 radiation (λ = 1.54060 Å). Fig. 4 shows the XRD pattern for the piezoelectric element deposited on a Si-substrate. The PZT material preferably had a composition of Pb(Zr0.58 Ti0.42 )O3 . Meanwhile, Pt3 Ti, Al0.983 Zr0.17 and Si were also detected. 2.3. Finite element analysis of PZT micro-actuator In order to test the driving capacity of this d31 -mode PZT actuator, a simple cantilever structure (SUS304) integrated with the PZT actuator was simulated by finite element analysis. This secondary actuator is located at the double sides of the cantilever beam and polarized in opposite direction (see Fig. 5 and Table 2). The two PZT elements are located 50 ␮m apart. When an electric field is applied across the thickness of the two PZT elements, parallel or anti-parallel to their polarization direction, one of the PZT coatings will Table 2 Dimensions of the SUS304 cantilever and PZT double-layer element Materials

Length, l (mm)

Width, w (mm)

Thickness, t (␮m)

SUS304 cantilever PZT double-layer element

7 1.2

0.32 0.32

50 1.5

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Displacement /um

10

20

30

40

1.5

1.5

1.0

1.0

0.5

0.5

0.0

0.0 10

20

30

40

Drive voltage/V

Fig. 6. Lateral tip displacement of the cantilever beam with different layers PZT actuators: (A) double-layer PZT, (B) single-layer PZT.

tip displacement of the two layers stack actuator is almost twice than that of the single layer actuator of the same overall thickness. In this study, finite element analyses were performed using the software ANSYS6.1 [20,21] since ANSYS provides a convenient tool to analyze piezoelectric behaviors of materials. The finite element simulation includes modal and electrostatic analysis. The modeling and related analysis results obtained by finite element analyses are shown in Fig. 7. The frequency of the sway mode is as high as >16.67 kHz. That can satisfy the requirement of high servo bandwidth of the high-density HDDs. The displacement sensitivity is also very important for high-density HDDs. The above design can get 0.9866 ␮m tip displacement, but only need ±15 V voltage drive. This means that the actuator had better achieve low power consumption and high displacement sensitivity. 2.4. Theoretical calculation

contract along x-direction and anther PZT coating will expand along x-direction. When the PZT coatings deform in opposite directions, a couple is generated about the dimple point (see Fig. 5), causing a lateral tip displacement of the suspension. Fig. 6 is comparison of the lateral tip displacements of the beam driven by PZT micro-actuator with different drive voltage as well as stacked actuators with different number of stack layers, while simulated by finite element method. The simulation results show that it is effective in increasing the tip displacement by increasing the number of stack layers of the PZT actuator. Then an effective way of increasing the lateral tip stroke response is to replace the single-layer PZT actuator with stacked PZT actuator. It can be seen from Fig. 6 that when the same applied voltage is produced, the

Piezoelectric bimorphs come in different versions due to differences in manufacturing methods. In this study, the PZT multi-layer micro-actuator model is depicted in Fig. 8(a). The arrows indicate the polarization direction of the PZT coatings. The model has three inner electrodes with each one connected to one of the poles of the voltage source. Application of an electric field across a piezoelectric material results in the deformation of that material (see Fig. 8(b)). If the electric field is applied in parallel with the polarization of the PZT multi-layer film, by convention along the z-axis, the PZT film will tend to contract in the planes perpendicular to the applied field, that is the x and y planes, and expand along the field axis, z. Conversely, if the electric field is applied in the direction anti-parallel with the polarization of the PZT film, it will tend to expand along

Fig. 7. The tip displacement of the PZT actuator/suspension assembly when a driving voltage of ±10 V was applied.

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333

Fig. 8. Diagram of the simple cantilever with PZT multi-layer thin film: (a) PZT multi-layer thin films model; (b) lateral tip displacement (δ) of the PZT model.

the planes perpendicular to the field, and contract along the direction of the field [22]. The crystal axis of a dielectrically polarized material is defined such that the polarization vector defines the 3- or z-direction [23]. The 1- and 2-directions (the xand y-directions) are then mutually perpendicular to the 3-direction. In general, the constituent equations of the piezoelectric effect given in tensor form are [22]: SI = SIJ E TJ + djI Ej , Di = diJ TJ + εTij Ej ,

(1)

where the strain tensor is denoted by SI , the dielectric displacement by Di , the compliance tensor at constant electric field by sij E . Meanwhile, the permittivity at constant stress is denoted by εij T , the piezoelectric tensor by djI , the stress tensor by TJ , the electric field by Ej . The mechanical and electromagnetic component are denoted by I, J and i, j, respectively. According to the boundary conditions: stress :

T1 = 0, T2 = T3 = T4 = T5 = T6 = 0,

electricfield :

E3 = 0, E1 = E2 = 0

(A)

S1 A = s11 E T1 A + d31 E3 , D3 A = d31 T1 B + e33 T E3

(3)

for the upper element which has the superscript A. The constituent equations for the lower element are

I, J = 1, 2, 3, 4, 5, 6, i, j = 1, 2, 3

Thus, the piezoelectric constituent equations for the bimorph bender of which the upper element (A) has its polarization parallel with the applied electric field and the polarization of the lower element (B) anti-parallel with the applied electric field are

(2)

(B)

S1 B = s11 E T1 B − d31 E3 , D3 B = −d31 T1 B + ε33 T E3

(4)

with a superscript B. From the constituent equation of portion B, it appears that the piezoelectric coefficient d31 is given a negative sign. In a static situation, where the bender has come to an equilibrium, forces FA and FB and moments MA and MB are present [24]. Because there is no movement in the x-direction, F A = F B , which implies that the superscripts A and B in F may be dropped. The strain in the lowest fiber of the portion A must be equal to the strain in the highest fiber

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in the portion B; otherwise there would be a discontinuity at the joint. These strain equations can be written as (5)–(7) FA + FB = 0

(5)

M +M −F t+F t =0 A

B

A

B

(6)

F B s11 E MBt F A s11 E MAt + − d31 E3 = + + d31 E3 (7) 2wt γIy 2wt γIy where γIy is the bending stiffness of each of the beam elements, s11 E the compliance tensor at constant electric field and d31 the piezoelectric constant. l, w, t are length, width, and thickness of each of the PZT sol–gel monolayer, respectively. The beam elements are joined over their entire length, so the radii of curvature of both sides are equal. From this we may conclude that 1 MA MB = = ρ γIy γIy

(8)

where ρ is the radii of curvature, γ the Young’s modules E , and I the moment of inertia: and is equal to 1/s11 y Iy =

w(2t)3 2wt3 = 12 3

(9)

and as portions A and B are identical in all respects except for the polarization, γIy is identical for them, which implies that MA = MB = M

(10)

Using Eqs. (5)–(10), we can write MA = MB = M = FB =

−2wtd31 E3 s11 E

2wt2 d31 E3 , s11 E

FA =

2wtd31 E3 , s11 E (11)

Because of d31 < 0, then M A = M B < 0, contrary to the direction of the said diagram. From Eq. (8) and the well known equation for the curvature of the bender, we can derive the curvature (1/ρ) of the bender y : γIy y = M ⇒ y =

M 3d31 E3 = γIy t

(12)

where y is the second derivative of the elastic curve y. Integrating once with respect to x gives the slope y as y =

3d31 E3 x t

3d31 E3 x2 2t

3d31 E3 l , t E3 t V = 2

α=

δ1 =

3d31 E3 l2 3d31 Vl2 = , 2t t2 (15)

where the applied voltage is denoted by V. In a similar way, for the single-layer PZT micro-actuator model with the same total thickness, we can deduce that δ2 =

3d31 Vl2 3d31 E3 l2 = , 2t 2t 2

V = E3 t

(16)

From the result of the integration we find the driving capacity of the two-layer PZT micro-actuator is almost twice that of the single layer actuator of same element thickness. It is evident that the d31 -type multi-layer structure is particularly effective in increasing the displacement/voltage sensitivity and resonance frequency of the dual-stage system.

3. Conclusion In this paper results on a PZT-based micro-actuators were presented. Thin-film PZT multi-layer actuators were designed and fabricated for high TPI hard disk servo system for quick and accurate positioning of the read/write head. Especially, thin-film PZT with multi-layer structure has many advantageous in acquiring larger electric field with lower applied voltage compared with the single layer thin-film PZT structure. On the other hand, a simple finite element model was developed which accurately replicated the piggyback PZT micro-actuator bonding to a SUS304 cantilever integrated with a d31 -mode PZT actuator. Using this model, the displacement/voltage sensitivity and resonance frequency of the suspension/actuator assembly were investigated. The results show that when a double-layer thin-film PZT micro-actuator is used, a applied voltage of ±15 V is sufficient to obtain 0.9866 ␮m tip displacement and high-resonance frequency over 16.67 kHz, yielding the required servo bandwidth (13 kHz) of more than several kHz. And in accordance with the results of FEM and theoretical calculation, the multi-layer PZT micro-actuator design has greater driving capacity than the single layer one.

(13)

and integrating once more gives the deflection at any position x y=

and slope at the tip of the double-layer PZT micro-actuator model, respectively:

(14)

In this example, for the rectangular micro-actuator, when we give the particular designation δ1 and the α for the deflection

Acknowledgements The authors would like to thank Dr. Ren Tianling and Dr. Duan Fangli at the Institute of Microelectronics of Tsinghua University and State Key Laboratory of Tribology of Tsinghua University, for instructions and discussions.

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References [1] W. Guo, T. Huang, C. Bi, K.T. Chang, T.S. Low, A high bandwidth piezoelectric suspension for high track density magnetic data storage devices, IEEE Trans. Magn. 34 (1998) 1907–1909. [2] Y. Soeno, S. Ichikawa, T. Tsuna, Y. Sato, I. Sato, Piezoelectric piggy-back microactuator for hard disk drive, IEEE Trans. Magn. 35 (1999) 983–987. [3] Y.M. Niu, W. Guo, G.X. Guo, H.O. Eng, K.K. Sivadasan, T. Huang, A PZT micro-actuated suspension for high TPI hard disk servo systems, IEEE Trans. Magn. 36 (5) (2000) 2241–2243. [4] Z.H. Wang, W.G. Zhu, X. Yao, d31 type inplane bending multilayer piezoelectric microactuators—a design concept and its applications, Sens. Actuat. 101 (2002) 262–268. [5] A. Nitin, W. Yossawee, Precision positioning using MEMS based microactuator, Mechatronics 12 (2002) 1213–1223. [6] L. Jiang, R.N. Miles, A passive damper for the vibration modes of the head actuator in hard disk drives, J. Sound Vibr. 220 (1999) 683–694. [7] M. Sasaki, T. Suzuki, E. Ida, F. Fujisawa, M. Kobayashi, H. Hirai, Track-following control of a dual-stage hard disk drive using a neuro-control system, Eng. Appl. Artif. Intell. 11 (1998) 707– 716. [8] X. Liu, J. Liu, C.K. Lim, Fem and experimental analysis of the actuator butterfly mode in a hard-disk drive, Mech. Syst. Signal Process. 17 (2003) 955–964. [9] M. Shiraishi, M.G. Yao, Method and apparatus for the physical and electrical coupling of a hard disk micro-actuator and magnetic head to a drive arm suspension, WO Patent 060 886 (2003). [10] H. Kueppers, T. Leuerer, U. Schnakenberg, W. Mokwa, M. Hoffmann, T. Schneller, U. Boettger, R. Waser, PZT thin films for piezoelectric microactuator applications, Sens. Actuat. A 97–98 (2002) 680– 684. [11] C.-C. Hsueh, T. Tamagawa, C. Ye, Sol–gel derived ferroelectric thin films in silicon micromachining, Int. Ferroelectr. 3 (1993) 21–32. [12] K. Hideki, M. Kaoru, Thin-film piezoelectric DSA for HDD, IEEE Trans. Magn. 38 (2002) 2186–2188. [13] K. Hideki, U. Hirokazu, O. Yuko, K. Hiroyuki, M. Kaoru, Maunfacturing process of piezoelectric thin-film dual-stage actuator and its reliability for HDD, IEEE Trans. Magn. 38 (2002) 2156– 2158. [14] D.F. Bahr, J.S. Robach, J.S. Wright, L.F. Francis, W.W. Gerberich, Mechanical deformation of PZT thin films for MEMS applications, Mater. Sci. Eng. A 259 (1999) 126–131. [15] N. Ledermann, P. Muralt, J. Baborowski, S. Gentil, K. Mukati, M. Cantoni, A. Seifert, N. Setter, {1 0 0}-Textured, piezoelectric Pb(Zrx , Ti1−x )O3 thin films for MEMS: integration, deposition and properties, Sens. Actuat. A 105 (2003) 162–170. [16] Q.Q. Zhang, S.J. Gross, S. Tadigadapa, T.N. Jackson, F.T. Djuth, S. Trolier-McKinstry, Lead zirconate titanate films for d33 mode cantilever actuators, Sens. Actuat. A 105 (2003) 91–97. [17] I.W. Rangelow, Reactive ion etching for high aspect ratio silicon micromachining, Surf. Coat. Technol. 97 (1997) 140–150. [18] C. Gui, M. De Boer, J.G.E. Gardeniers, Fabrication of multi-layer substrates for high aspect ratio single crystalline microstructures, Sens. Actuat. A 70 (1998) 61–66. [19] H. Kueppers, M. Hoffmann, T. Lenerer, T. Schneller, U. Boettger, R. Waser, W. Mokwa, U. Schankenberg, Basic investigations on a

[20] [21]

[22] [23]

[24]

335

piezoelectric bending actuator for micro-electro-mechanical applications, Int. Ferroelectr. 35 (2001) 269–281. ANSYS, Structure Analysis Guide Release, vol. 5.4, Canonburg, ANSYS, Inc., PA, 1997. D. de Bhail´ıs, C. Murray, M. Duffy, J. Alderman, G. Kelly, S.C. Ó Mathúna, Modelling and analysis of a magnetic microactuator, Sens. Actuat. A 81 (2000) 285–289. J.G. Smits, S.I. Dalke, T.K. Cooney, The constituent equations of piezoelectric bimorphs, Sens. Actuat. A 28 (1991) 41–61. S.H. Wang, Z.H. Wang, X. Yao, Piezoelectric composite suspension for high density rigid disk drives, Piezoelectr. Acoustoopt. 22 (2000) 373–375. W.A. Nash, Strength of Materials, McGraw-Hill, New York, 1972, p. 809.

Biographies Yang Jing received his BSc degree in 1994 from Luoyang Institute of Technology, China and PhD in 1989 from Beijing Institute of Technology, China. Currently, he is a postdoctor at Tsinghua University, China. He has published widely in international journals. His research interests include electronic materials, piezoelectric ceramic materials, thin films, and ferroelectrics, etc. Now, his main research interests focus on preparation and characterization of various electronic ceramics and ferroelectric films; design, fabrication and reliability assessment of micro-actuators for dual-stage actuator systems for high-density hard disk drives. Jianbin Luo is a professor in Tsinghua University, is the vice director of the State Key Laboratory of Tribology, China. He got his PhD degree from Tsinghua University in 1994, master in 1988, and bachelor in 1982. Since 1991, he has been working on nano-tribology in Tsinghua University and published more than 130 papers in the fields of tribology. He won the following awards: Chinese National Natural Science Prize, 2nd, 2001; Natural Science Prize of Chinese Universities, 1st, 2001; Chinese Outstanding Youth Award, 2000; Chinese National Invention Prize, 3rd, 1996; Chinese Education Ministry Prize for Scientific Advance, 1st, 1996; Shanxin Province Prize for Natural Scientific Thesis, 3rd grade, 1991. Xiaoxing Yi was born in 1957. She graduated from the Beijing Radio and TV University in electronics department in 1982. Since 1976, she has been with the Institute of Acoustics, Chinese Academy of Sciences. At present, she is a senior engineer, her research and development activity has been on piezoelectric ceramic materials; in particular, on modified lead metaniobate (modificative PbNb2 O6 ) compositions and nano-piezoelectric materials. She is a member of special ceramic sub-committee of Chinese ceramic society. In the past 28 years, she has co-authored more than 10 refereed papers, reports and patents in the field of piezoelectric ceramics. She received the award of third grade, named developing sciences & technology in 1998. Xin Gu received his BSc degree in 2000 from the State Key Laboratory of Tribology, Tsinghua University, China. Currently, he is a graduate student at Tsinghua University, China. Now, his main research interests focus on design, fabrication and reliability assessment of micro-actuators for dual-stage actuator systems for high-density hard disk drives.