教育部補助博士班研究生出席國際會議報告

序號：

姓

名

周正賢 會議期間 2003.03.09~2003.03.12

會議

名稱

中文：國際積體鐵電會議

英文：International Symposium on Integrated Ferroelectrics

受補

助項

目

機票費：__39,000________ 生活費：__6,367________

註冊費：__3,121________合計總金額：_48,488_________

出國

報

告：

2003 ISIF

國際積體鐵電會議心得

材料所博士班 d907515 周正賢

指導教授:黃金花

前言

三月八號下午四點，搭乘華航往洛杉磯的班機飛美，參加 2003

年的國際積體鐵電會議(International Symposium of Integrated

Ferroelectrics,ISIF2003)，會議於三月九日到三月十二日於科羅

拉多州的柯泉市舉行，一行人在十一個小時的長途飛行抵達洛杉磯

後，正式踏上美國的土地，在機場的安檢相當嚴格，我想一方面洛

杉磯是全美大城，並且最近又逢美伊開打的緊張時刻，使得機場警

衛們如臨大敵，出海關的時間也稍長。

於洛杉磯機場再轉機至科泉市(Colorado Springs)，美西的天

然地形令人嘆為觀止，在飛機上可看到落磯山脈後，有沙漠，也有

像大峽谷一般的地形，這些地形有一個共通點，人煙稀少。再往北

接近丹佛時看到高原積雪未融，兩個多小時的飛行接近終點則終於

看到了兩處人口較多的地方，一是丹佛市，另一則是科泉市。出機

場後搭車前往會議地點 Broadmoor Hotel，感覺上科泉市很像電影

中的小城鎮，住家並不密集。

至 Broadmoor Hotel 放置行李之後，便前往會場註冊，參加這

次的國際積體鐵電會議。

會議心得

開始的 Invited talk 是鐵電記憶體的趨勢，是想將系統整合在

單晶片上。Invited talk 之後，一行人便分別至三個演講廳參加不

同議題的報告，於是選擇了與微機電較相關的議題，以下便簡述一

些與論文本身相關的報告以及一些微機電技術的相關應用。

利用微機電的技術，Switzerland 的 F.Calame11等人可以做成

約數十到數百微米見方大小的加熱板如圖一，局部加熱 PZT 壓電材

料使其成結晶相；這樣的想法是因為 PZT 使用 Spin Coating 成相的

溫度大約在 6000C 如圖二，高溫可能會導致金屬擴散形成短路使得元

件失

圖一 微加熱板 圖二 局部 PZT 成相

效，利用微加熱板可在局部加熱而不致影響元件其餘部分。

做法則是先在矽基板上鍍上SiO2及 Si3N4以提供足夠的機械強度

及應力補償的效果，再鍍上 Ta5Si3的加熱材料，再繼續鍍上應力緩

衝層 Ti/Si/SiO2，將 Pt 電極鍍上並將 Contact Pade 拉出如圖三，

最後鍍覆上 PZT，在 800mW 的數入功率下可達到約 6500C 的加熱效

果，以 X-Ray 的結果檢驗可得到 PZT(111)及(100)的結晶相如圖四，

證明了此種做法的可行性。

圖三 微加熱板結構 圖四 PZT 之 XRD

傳統 Sol-gel 鍍覆 PZT 的優點是易於控制成分，大面積鍍覆複

雜表面形貌的試片，但要微影蝕刻 PZT 薄膜時會遇到兩個問題：一

是燒結時因為薄膜收縮所造成之孔洞，二是由於 PZT 的化學惰性造

成蝕刻不易。Bedfordshire 的 S.Marson2等人利用一種光敏

(Photosensitive)添加 Nb 的前驅物(precursor)，先預烤 PZT 薄膜，

經過曝光之後，此前驅物在某些有機溶劑中的溶解度會降低，流程

如圖五所示，因此曝光過的區域則會被選擇性的留下如圖六。

圖五 微影製程流程圖 圖六選擇性留下之 PZT

南韓的 Sun Wook Kim3,4等人利用磁控濺鍍製作 SiO2/W 交替的聲

波反射層，再以磁控濺鍍製備優選取向的壓電層 ZnO，以 AFM 檢查表

面的粗糙度為 15.6Å，利用 1 port 的觀念製作體聲波元件，聲波反

射層的製備薄膜需要極佳之均勻度，否則反射之相位會偏移，利用

磁控濺鍍可得到均勻度佳之薄膜，另外壓電層 ZnO 之製備在不同工

作壓力下的結果以 15m torr,213W 功率下得到之 ZnO 之優選取向程

度較高，最後以微波量測之結果由 Smith Chart 可得到其並聯共振

與串聯頻率及，並由此可算出其共振器之 Q值，圖七為會場海報，

其主要重點為材料部份能做到均勻度佳之 ZnO 並有優選取向。

圖七 會場海報＂Characteristics of ZnO thin film by RF

magnetron sputtering for FBAR applications＂

圖八為 Sun Wook Kim 等人另一篇論文，重點在於體聲波元件之

製作及微波特性量測。

圖八 會場海報＂Fabrication of ZnO based Film Bulk

Acoustic Resonator for GHz frequencies＂

北京清華大學的 Hong-Jing Zhao5等人則是以面蝕刻(surface

micromachining)的做法製作體聲波元件，如流程圖所示將多晶矽犧

牲層蝕刻掉之後形成懸臂結構如圖九，製作流程圖如圖十所示。

圖九 元件結構示意圖 圖十 面蝕刻製程流程圖

此種結構可消除較厚支撐層的影響並減少 Cross Talk，並利用

SiO2 覆蓋在上電極之上以調整共振頻率，濾波器的中心頻率為

2GHz，品質因子為 80，濾波器如圖十一所示。

圖十一 以面蝕刻製作之濾波器

Hong-Jing Zhao6等人在另一篇發表中則以體蝕刻(bulk

micromachining)的做法製作體聲波元件如圖十二，製作流程圖如圖

十三所示。先在基板兩側鍍上蝕刻阻擋層，依序鍍下電極及壓電層，

再以 NaOH 蝕刻 Si，其共振器單元為圖十四，濾波器中心頻率為

2.0GHz，頻寬為 150MHz，品質因子為 80，濾波器如圖十五所示。

圖十二 元件結構示意圖 圖十三 體蝕刻製程流程圖

圖十四 體蝕刻製作之共振器 圖十五 體蝕刻製作之濾波器

後記

第一次到國外參加學術會議，心情是有點緊張，但到了會議地

點，感覺和國內參加過的會議很熟悉，只是臉孔換了，語言換成英

文溝通。

這次到了美國收穫是蠻多的，可以與這麼多的學者面對面的進

行討論，以及領略了美國的地大物博;這次的會議讓人收穫良多，各

國的論文發表讓我們知道目前最頂尖的研究水平，也讓我們知道要

加緊努力或是可以超越的研究方向，希望下次出國參加會議之前我

們可以提升自己的研究水準，與最頂尖的實驗室可相比擬。

與林諭男老師及發表論文＂FABRICATION OF PZT-BASED THIN FILM BULK ACOUSTIC WAVE RESONATORS USING MULTILAYER REFLECTOR＂海報合照

Reference

[1]F.Calame, J.Baborowski, S.Gentil, N.Ledemann,and P.Muralt＂Local

growth of sol-gel films by means of micro hot-plates＂,ISIF 2003 Book

of abstracts

[2]S.Marson, R.A. Dorey, Q.Zhang, R.W. Whatmore＂Thick PZT

Micro-Features obtained by direct patterning of photosensitive precursor

solutions＂,ISIF 2003 Book of abstracts

[3] Sun Wook Kim, Seung Man Lim, Soo Gil Kim, Neung Heon Lee,and Yong

Hwa Shin＂Characteristics of ZnO thin film by RF magnetron sputtering

for FBAR applications＂,ISIF 2003 Book of abstracts

[4] Sun Wook Kim, Seung Man Lim, Soo Gil Kim, Neung Heon Lee,and Yong

Hwa Shin＂Fabrication of ZnO based Film Bulk Acoustic Resonator for GHz

frequencies＂,ISIF 2003 Book of abstracts

[5] Hong-Jing Zhao, Tian-Ling Ren, Peng Cong, Jian-She Liu, Li-Tian Liu,

Zhi-Jian Li＂BAW Resonators and Filters using surface

micromachining＂,ISIF 2003 Book of abstracts

[6] Hong-Jing Zhao, Tian-Ling Ren, Jian-She Liu, Li-Tian Liu, Zhi-Jian

Li＂Thin Film Bulk Acoustic Resonators and Filters using PZT/Pt based

structures＂,ISIF 2003 Book of abstracts

發表

論文

全

文：

FABRICATION OF PZT-BASED THIN FILM BULK ACOUSTIC WAVE RESAONTORS USING MULTILAYER REFLECTOR

Cheng Hsien Chou1, Shih-Yen Liu1, Jin-Hua Huang1 and I-Nan Lin2

1Department of Materials Science & Engineering, National Tsing-Hua University, 2Materials Science Center, National Tsing-Hua University, Hsinchu,

Taiwan 300, R.O. C.

Thin film bulk acoustic wave resonators (FBARs), possessing high quality factor resonant characteristics at microwave frequency regime, have been intensively investigated in recent years due to the potential for integration of these devices in monolithic microwave integrated circuits (MMIC). One of the key issues in designing the FBARs structure is the minimization of acoustic wave loss through the substrates. Conventional technique for such an end is to create air boundary by using either surface or bulk micro-machining (MEMS) process. Another approach is to fabricate solidly mounted resonator (SMR), on which piezoelectric resonator layer was deposited. In the meantime, the high electromechanical coupling coefficient in Pb(Zr,Ti)O3 (PZT) materials offers the possibility of realizing wide bandwidth filter. In this paper, we review our recent work on the application of PZT as piezoelectric layer in thin film bulk acoustic wave resonators (FBARs). First of all, SiO2 and Si3N4layers, with thickness of quarter acoustic wavelength, were sequentially deposited on silicon (Fig. 1), forming SMR substrates. The acoustic absorbing efficiency for SiO2/Si3N4 pairs was examined. PZT films with highly preferred orientation were then grown on thus obtained SMR substrates, using metallo-organic decomposition (MOD) process. Special techniques, such as utilization of nano-sized powder incorporated precursors and highly textured buffer layer, were adopted to modify the characteristics of the PZT films. Variation of the acoustic properties of the PZT films with their material’s parameters was systematically examined. The corresponding effect of these characteristics on the frequency response of thus obtained FBARsdevices was also studied. Keywords : FBAR, PZT, SMR, MOD, resonator Introduction

The FBARs show great ability in miniaturizing wireless communication systems. Among the various advantages of FBARs, the IC-compatible process of FBARs offer a single-chip solution for a personal communication system.

In this paper we review our recent work on the application of PZT as the piezoelectric layer in FBARs. The high electromechanical coupling coefficients in PZT offers the possibility of realizing wide bandwidth filters. It is shown possible to incorporate PZT into a multilayer reflector structure by Ti buffer layer that avoids the crazing that occurs when PZT is deposited directly on SiO2.

Experimental Procedure From transmission line theory, we can use low/high impedance quarter

wavelength layer as impedance inverter. It is possible to evaluate the input impedance using this formula:

L

n

high

lowin ZZ

ZZ2

⎟⎟⎠

⎞⎜⎜⎝

⎛= ,

Here Zlow and Zhigh means acoustic impedance of SiO2 and Si3N4 respectively, the acoustic reflection efficiency will tend to unity when using more than 5 SiO2/Si3N4 pairs. According to the acoustic constant such as stiffness constant and mass density of SiO2 and Si3N4 , one can obtain the acoustic velocity. Table 1 showed the acoustic constant and the needed thickness of each layer. We used Si(100) as substrate and deposited SiO2 and Si3N4 alternatively by sputtering process. The sputtering system was pumped down to a base pressure below 6×10-7 torr before admitting the gas in. The films were grown at 5m torr pressure with a power of 150W.

An additional layer of Ti is deposited on multilayer reflector for increasing the adhesion of PZT and SiO2. The reason for doing this is without Ti buffer layer, the surface will become rough and cracked, increasing the possibility of short-circuits.

Metal-Organic deposition(MOD) process was used to fabricate Pb(Zr,Ti)O3 (PZT) ferroelectric thin films. Initially, PZT films were spin-coated on multilayer reflector substrates from carboxylate-based solutions by annealing at 550℃. The total layers used to fabricate PZT-based thin film bulk acoustic wave resonators is shown in Fig 1. In this structure the 5 SiO2/Si3N4 pairs were first deposited on silicon wafer like Fig 2. And then the bottom electrode was deposited and patterned. The piezoelectric layer was prepared by MOD process. Finally the top electrode was also patterned by wet etching process. The photograph of Fig 3 showed the FBAR resonator area after photo-lithography process. The crystalline phases, microstructure, the thickness of the films were characterized by an Rigaku X-ray diffractometer with Cu Kα, a scanning electron microscope(Jeol 5400) respectively. The microwave property was measured by HP8722ES network analyzer using Coplanar Waveguide (CPW) configuration. Results and discussion Fig 4 shows XRD patterns of the PZT thin films deposited on multilayer reflector substrate and annealing at 5500C for 30min. All the PZT films consists of perovskite phase with no pyrochlore phase. The hysterisis loop of PZT film was shown in Fig 5. It can be seen that the film

displayed ferroelectric properties. The remanent polarization and coercive field (Ec) were 11.7 μC/cm2 and 155.0 kV/cm, respectively. At Fig 6 the leakage current of PZT FBARs slowly increases to 10-6 A/cm2at 10V.

The results presented here have shown that PZT FBAR resonators can be produced that are able to operate above 1 GHz. The measured bandwidth of PZT FBAR resonators were greater than AlN or ZnO FBAR resonators. The small size of PZT resonators were highly desireable for incorporation into mobile phones. We Conclusions The PZT thin films were successfully prepared on SiO2 /Si3N4 substrate by a MOD technique. The remanent polarization (Pr) and coercive field (Ec) of PZT thin films were 11.7 mC/cm2 and 155.0 kV/cm, respectively.

References:

1. K.M. Lakin, K.T. Mccarron, and R.E. Rose “Solidly Mounted Resonators and Filters”Ultrasonics Symposium., 1995, pp. 905-908

2. Q.X. Su, P.B. Kirby, E. Komuro, M. Imura, Q. Zhang, and R.W. Whatmore“Thin films bulk acoustic resonators and filters using ZnO and Lead-Zirconium-Titante thin films”IEEE Trans. on Microwave Theory and Techniques, Vol. 49, no 4 (2001), pp.769-778

Material Acoustic Velocity(m/s) Acoustic Impedance(kg/m2s) 1/4 λ (μm)

SiO2 5,800 12759310 0.591

Si3N4 6,700 20758130 0.683

Table 1

Fig 1

Fig2

20 30 40 50 60

0

100

200

300

400

500

600

700

800

PZT(211)

PZT(200)

Pt(111)

PZT(111)

PZT(110)

PZT(100)

Inte

nsity

2q

PZT FBAR

Fig 4

-800 -600 -400 -200 0 200 400 600 800

-40

-30

-20

-10

0

10

20

30

40

PZT FBAR

Electric field(kV/cm)

Pola

rizat

ion(m

C/c

m2 )

Fig 5

0 2 4 6 8 10

1E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

Log(

I)

Voltage

PZT FBAR

Fig 6

Fig 7

受補助之學生請於回國後將此表填妥 mail 至 mailto:eclue@mx.nthu.edu.tw 信箱