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Characterization of epitaxial GaAs MOS capacitors using atomic layer-deposited TiO2/Al2O3 gate stack: study of Ge auto-doping and p-type Zn doping Nanoscale Research Letters 2012, 7:99 doi:10.1186/1556-276X-7-99 Goutam KUMAR Dalapati (dalapatig@imre.a-star.edu.sg) Terence KIN SHUN Wong (EKSWONG@ntu.edu.sg) Yang Li (younglee.leon@hotmail.com) C K Chia (ck-chia@imre.a-star.edu.sg) Anindita Das (an.indita@yahoo.com) Chandreswar Mahata (chandreswar@gmail.com) Han Gao (h-gao@imre.a-star.edu.sg) Sanatan Chattopadhyay (c_sanatan@yahoo.com) Manippady KRISHNA Kumar (kumarm@imre.a-star.edu.sg) Hwee LENG Seng (debbie-seng@imre.a-star.edu.sg) Chinmay KUMAR Maiti (ckm@ece.iitkgp.ernet.in) Dong ZHI Chi (dz-chi@imre.a-star.edu.sg) ISSN 1556-276X Article type Nano Express Submission date 24 November 2011 Acceptance date 2 February 2012 Publication date 2 February 2012 Article URL http://www.nanoscalereslett.com/content/7/1/99 This peer-reviewed article was published immediately upon acceptance. 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This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1 Characterization of epitaxial GaAs MOS capacitors using atomic layer-deposited TiO 2 /Al 2 O 3 gate stack: study of Ge auto-doping and p-type Zn doping Goutam Kumar Dalapati* 1 , Terence Kin Shun Wong 2 , Yang Li 2 , Ching Kean Chia 1 , Anindita Das 3,4 , Chandreswar Mahata 5 , Han Gao 1 , Sanatan Chattopadhyay 3,4 , Manippady Krishna Kumar 1 , Hwee Leng Seng 1 , Chinmay Kumar Maiti 5 , and Dong Zhi Chi 1 1 Institute of Materials Research and Engineering, A*STAR, (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602, Singapore 2 School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore 3 Department of Electronic Science, University of Calcutta, 92-A. P. C. Road, Kolkata 700 009, India 4 Centre for Research in Nanoscience and Nanotechnology, (CRNN), University of Calcutta, JD- 2 Sector III, Kolkata 700 098, India 5 Department of Electronics and ECE, Indian Institute of Technology, Kharagpur 721302, India *Corresponding author: dalapatig@imre.a-star.edu.sg Email addresses: GKD: dalapatig@imre.a-star.edu.sg TKSW: EKSWONG@ntu.edu.sg YL: younglee.leon@hotmail.com CKC: ck-chia@imre.a-star.edu.sg AD: an.indita@yahoo.com CM: chandreswar@gmail.com HG: h-gao@imre.a-star.edu.sg SC: Capacitors and Dielectrics Capacitors and Dielectrics Bởi: OpenStaxCollege A capacitor is a device used to store electric charge Capacitors have applications ranging from filtering static out of radio reception to energy storage in heart defibrillators Typically, commercial capacitors have two conducting parts close to one another, but not touching, such as those in [link] (Most of the time an insulator is used between the two plates to provide separation—see the discussion on dielectrics below.) When battery terminals are connected to an initially uncharged capacitor, equal amounts of positive and negative charge, +Q and – Q, are separated into its two plates The capacitor remains neutral overall, but we refer to it as storing a charge Q in this circumstance Capacitor A capacitor is a device used to store electric charge 1/14 Capacitors and Dielectrics Both capacitors shown here were initially uncharged before being connected to a battery They now have separated charges of +Q and – Q on their two halves (a) A parallel plate capacitor (b) A rolled capacitor with an insulating material between its two conducting sheets The amount of charge Q a capacitor can store depends on two major factors—the voltage applied and the capacitor’s physical characteristics, such as its size The Amount of Charge Q a Capacitor Can Store The amount of charge Q a capacitor can store depends on two major factors—the voltage applied and the capacitor’s physical characteristics, such as its size A system composed of two identical, parallel conducting plates separated by a distance, as in [link], is called a parallel plate capacitor It is easy to see the relationship between the voltage and the stored charge for a parallel plate capacitor, as shown in [link] Each electric field line starts on an individual positive charge and ends on a negative one, so that there will be more field lines if there is more charge (Drawing a single field line per charge is a convenience, only We can draw many field lines for each charge, but the total number is proportional to the number of charges.) The electric field strength is, thus, directly proportional to Q Electric field lines in this parallel plate capacitor, as always, start on positive charges and end on negative charges Since the electric field strength is proportional to the density of field lines, it is also proportional to the amount of charge on the capacitor 2/14 Capacitors and Dielectrics The field is proportional to the charge: E ∝ Q, where the symbol ∝ means “proportional to.” From the discussion in Electric Potential in a Uniform Electric Field, we know that the voltage across parallel plates is V = Ed Thus, V ∝ E It follows, then, that V ∝ Q, and conversely, Q ∝ V This is true in general: The greater the voltage applied to any capacitor, the greater the charge stored in it Different capacitors will store different amounts of charge for the same applied voltage, depending on their physical characteristics We define their capacitance C to be such that the charge Q stored in a capacitor is proportional to C The charge stored in a capacitor is given by Q = CV This equation expresses the two major factors affecting the amount of charge stored Those factors are the physical characteristics of the capacitor, C, and the voltage, V Rearranging the equation, we see that capacitance C is the amount of charge stored per volt, or Q C = V Capacitance Capacitance C is the amount of charge stored per volt, or Q C = V The unit of capacitance is the farad (F), named for Michael Faraday (1791–1867), an English scientist who contributed to the fields of electromagnetism and electrochemistry Since capacitance is charge per unit voltage, we see that a farad is a coulomb per volt, or 1F= 1C V 3/14 Capacitors and Dielectrics A 1-farad capacitor would be able to store coulomb (a very large amount of charge) with the application of only volt One farad is, thus, a very large capacitance Typical capacitors range from fractions of a picofarad (1 pF = 10–12 F) to millifarads (1 mF = 10–3 F) [link] shows some common capacitors Capacitors are primarily made of ceramic, glass, or plastic, depending upon purpose and size Insulating materials, called dielectrics, are commonly used in their construction, as discussed below Some typical capacitors Size and value of capacitance are not necessarily related (credit: Windell Oskay) Parallel Plate Capacitor The parallel plate capacitor shown in [link] has two identical conducting plates, each having a surface area A, separated by a distance d (with no material between the plates) When a voltage V is applied to the capacitor, it stores a charge Q, as shown We can see how its capacitance depends on A and d by considering the characteristics of the Coulomb force We know that like charges repel, unlike charges attract, and the force between charges decreases with distance So it seems quite reasonable that the bigger the plates are, the more charge they can store—because the ...ORIGINAL PAPER Open Access Structure and electrical properties of sputtered TiO 2 /ZrO 2 bilayer composite dielectrics upon annealing in nitrogen Ming Dong 1 , Hao Wang 2* , Cong Ye 2* , Liangping Shen 2 , Yi Wang 2 , Jieqiong Zhang 2 and Yun Ye 2 Abstract The high-k dielectric TiO 2 /ZrO 2 bilayer composite film was prepared on a Si substrate by radio frequency magnetron sputtering and post annealing in N 2 at various temperatures in the range of 573 K to 973 K. Transmission electron microscopy observation revealed that the bilayer film fully mixed together and had good interfacial property at 773 K. Metal-oxide-semiconductor capacitors with high-k gate dielectric TiO 2 /ZrO 2 /p-Si were fabricated using Pt as the top gate electrode and as the bottom side electrode. The largest property permittivity of 46.1 and a very low leakage current density of 3.35 × 10 -5 A/cm 2 were achieved for the sample of TiO 2 /ZrO 2 /Si after annealing at 773 K. Introduction High dielectric constant [high-k] materials have been researched for a few years in material sc ience and have been applied firstly in Intel’ s 45 nm MOSFET in 2007. Nowadays, for the demand of the next generation devices for sub-22 nm technology nodes, expect that high-k materialssuchasHfO 2 ,ZrO 2 ,Ta 2 O 5 , and rare earth oxides are extensively researched, and binary oxi- des of high-k materials become more attractive and are expected to be utilized in the future ultra large scale integrated circuit [1-8]. Among them, ZrO 2 has a rela- tively high permittivity, large band gap, and good ther- mal and chemical stabilities. TiO 2 is a high-k material with a very high permittivity of about 80 [9]. In order to improve the permittivity of ZrO 2 , the feasible way is to fabricate ZrO 2 -TiO 2 composite films. Meanwhile, as a composite thin film, the addition of TiO 2 can improve the crystallization temperature [10,11]. As ZrO 2 -TiO 2 binary oxides, a nanolaminate structure which can tailor the electrical properties of dielectric stacks has many applications such as MIM diodes, storage capacitors, non-volatile memories, and transparent thin film transis- tors; thus, the nanolaminated ZrO 2 -TiO 2 high dielectric constant thin film is worth studying Concerning high-k stacks on silicon, the interface has an important role to influence the device. Normally, it is often thought that TiO 2 is easier to react with the Si substrate which may deteriorate the property of the device, and thus, TiO 2 /ZrO 2 /Si stacks may have better electrical characterization [12-14]. In the present work, metal-oxide-semiconductor [MOS] capacitors with high- k gate dielectric TiO 2 /ZrO 2 /p-Si were fabricated using Pt as the top gate electrode and as the bottom side elec- trode. The structure and electrical property of the TiO 2 / ZrO 2 /Si stack are studied. Experimental details ZrO 2 and TiO 2 thin films were grown onto p-type (100) Si (P~10 15 cm -3 ) to fabricate TiO 2 /ZrO 2 /Si stacks by radio frequency magnetron sputtering at room tempera- ture. Pure ZrO 2 (99.999%) and TiO 2 (99.999%) ceramic targets (50 mm in diameter) were used as the sputtering targets. The sputtering power of ZrO 2 and TiO 2 are 60 W and 30 W, respectively. Pure argon (99.999%) with 30 cm 3 /min flow rate controlled by a mass flow control- ler was used as sputtering gas, and the base pressure of the vacuum chamber is about 3 × 10 -5 Pa. Sputtering was carried out at a pressure of 0.3 Pa. As for the deposited TiO 2 /ZrO 2 /Si stacks, post Journal of Physical Science, Vol. 19(1), 53–62, 2008 53 Synthesis and Characterization of Bismuth Tantalate Binary Materials for Potential Application in Multilayer Ceramic Capacitors (MLCC) K.B. Tan*, F.G. Anna and Z. Zainal Chemistry Department, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Malaysia *Corresponding author: tankb@science.upm.edu.my Abstract: The single phase bismuth tantalate (BiTaO 4 ) was successfully synthesized by conventional solid-state method at sintering temperature 1100 o C. This material crystallized in a triclinic system, space group Pī with a = 7.6585 Ǻ, b = 5.5825 Ǻ, c = 7.7795 Ǻ, α = 90.03 o , β = 77.04 o and γ = 86.48 o , respectively. The electrical properties of BiTaO 4 were characterized by AC impedance analyzer, HP4192 at temperature ranging from 25 o C–850 o C over frequency range of 5–13 MHz. The sample was highly resistive as the conductivities were unlikely to be determined below 550 o C. On the other hand, BiTaO 4 exhibited moderate dielectric constant, ε r = 47 at ambient temperature in the frequency region of 1 MHz and near zero temperature coefficient of capacitance (TCC), 0.00022, making it a potential candidate for multilayer ceramic capacitors (MLCC). Keywords: solid-state method, electroceramics, dielectric constant, AC impedance spectroscopy Abstrak: Fasa tunggal bismut tantalat (BiTaO 4 ) telah disintesiskan secara kaedah keadaan pepejal pada suhu 1100 o C. Bahan ini berkristal dalam sistem triklinik, kumpulan ruang Pī dengan a = 7.6585 Ǻ, b = 5.5825 Ǻ, c = 7.7795 Ǻ, α = 90.03 o , β = 77.04 o dan γ = 86.48 o . Sifat elektrik telah dikaji dengan penggunaan impedans AC, HP4192 dalam lingkungan suhu 25 o C–850 o C daripada frekuensi 5–13 MHz. Sampel ini mempunyai kerintangan yang tinggi, dan kekonduksian adalah tidak mungkin ditentukan pada suhu bawah 550 o C. Sementara itu, BiTaO 4 menunjukkan pemalar dielektrik, ε r = 47 pada suhu sekitar dalam frekuensi 1 MHz dan juga pekali suhu bagi kapasitans (TCC), 0.00022 menyebabkan kesesuaian dijadikan sebagai kapasitor seramik berlapisan (MLCC). Kata kunci: kaedah keadaan pepejal, elektroseramik, pemalar dielektrik, spektroskopi impedans AC 1. INTRODUCTION Bismuth derivatives have received tremendous research interests due to their technological importance in various applications ranging from oxide ion Synthesis and Characterization of BiTaO 4 54 conductors, catalysts, band-pass filters, radio frequency applications and others. 1–5 The interesting properties are anticipated at the helm of bismuth powder due to its volatile, reactive characteristic and relatively low firing temperature in forming binary or ternary materials with other elements, e.g. bismuth vanadates, bismuth niobates or even structurally complex Bi-based pyrochlores. 3–7 However, functionality of these advanced ceramics always relies on compositional variation, control and processing that require better understanding through knowledge advancement in multi-disciplinary. Long gone are the days of integrating active or passive components onto the substrate using conventional printed circuit board (PCB) technique, which tends to be replaced by multilayer ceramic technology. This satisfies the trend of miniaturization and high functionality of modern electronic devices as green ceramic tapes of different materials serving different passive functions are laminated and co-fired at a lower firing temperature. 8 Therefore, compatibility of desired materials with electrodes, in particularly low melting temperature silver or gold electrode is of utmost attention prior to prototype testing or commercial applications. Of particular interest in electroceramics is bismuth based dielectrics which possess low-firing temperature; and have been extensively studied for MLCC. 5,9–10 Previous works have shown that, BiTaO 4 is a good dielectric material with high dielectric CHAPTER 5 CONDUCTORS, DIELECTRICS, AND CAPACITANCE In this chapter we intend to apply the laws and methods of the previous chapters to some of the materials with which an engineer must work. After defining current and current density and developing the fundamental continuity equation, we shall consider a conducting material and present Ohm's law in both its microscopic and macroscopic forms. With these results we may calculate resis- tance values for a few of the simpler geometrical forms that resistors may assume. Conditions which must be met at conductor boundaries are next obtained, and this knowledge enables us to introduce the use of images. After a brief consideration of a general semiconductor, we shall investigate the polarization of dielectric materials and define relative permittivity, or the dielectric constant, an important engineering parameter. Having both conduc- tors and dielectrics, we may then put them together to form capacitors. Most of the work of the previous chapters will be required to determine the capacitance of the several capacitors which we shall construct. The fundamental electromagnetic principles on which resistors and capaci- tors depend are really the subject of this chapter; the inductor will not be intro- duced until Chap. 9. 119 | | | | ▲ ▲ e-Text Main Menu Textbook Table of Contents 5.1 CURRENT AND CURRENT DENSITY Electric charges in motion constitute a current. The unit of current is the ampere (A), defined as a rate of movement of charge passing a given reference point (or crossing a given reference plane) of one coulomb per second. Current is symbo- lized by I, and therefore I dQ dt 1 Current is thus defined as the motion of positive charges, even though conduc- tion in metals takes place through the motion of electrons, as we shall see shortly. In field theory we are usually interested in events occurring at a point rather than within some large region, and we shall find the concept of current density, measured in amperes per square meter (A/m 2 ), more useful. Current density is a vector 1 represented by J: The increment of current ÁI crossing an incremental surface ÁS normal to the current density is ÁI J N ÁS and in the case where the current density is not perpendicular to the surface, ÁI J Á ÁS Total current is obtained by integrating, I S J Á dS 2 Current density may be related to the velocity of volume charge density at a point. Consider the element of charge ÁQ v Áv v ÁS ÁL, as shown in Fig. 5:1a. To simplify the explanation, let us assume that the charge element is oriented with its edges parallel to the coordinate axes, and that it possesses only an x component of velocity. In the time interval Át, the element of charge has moved a distance Áx, as indicated in Fig. 5:1b. We have therefore moved a charge ÁQ v ÁS Áx through a reference plane perpendicular to the direction of motion in a time increment Át, and the resultant current is ÁI ÁQ Át v ÁS Áx Át As we take the limit with respect to time, we have ÁI v ÁSv x 120 ENGINEERING ELECTROMAGNETICS 1 Current is not a vector, for it is easy to visualize a problem in which a total current I in a conductor of nonuniform cross section (such as a sphere) may have a different direction at each point of a given cross section. Current in an exceedingly fine wire, or a filamentary current, is occasionally defined as a vector, but we usually prefer to be consistent and give the direction to the filament, or path, and not to the current. | | | | ▲ ▲ e-Text Main Menu Textbook Table of Contents where v x represents the x component of the velocity v: 2 In terms of current density, we find J x v v x and in general J v v 3 This last result shows very clearly that charge in motion constitutes a current. We call this type of current a convention current, and J or v v is the convection current density. Note that the convection current density is related linearly to charge density as well as to HIGH-K DIELECTRICS IN METAL INSULATOR METAL (MIM) CAPACITORS FOR RF APPLICATIONS PHUNG THANH HOA NATIONAL UNIVERSITY OF SINGAPORE 2011 HIGH-K DIELECTRICS IN METAL INSULATOR METAL (MIM) CAPACITORS FOR RF APPLICATIONS PHUNG THANH HOA (B.ENG., NATIONAL UNIVERSITY OF SINGAPORE) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2011 Acknowledgements A Ph.D candidature is a challenging path which is filled with excitements and also plenty of disappointing moments, and I would not have reached this stage without the help, support and guidance from a group of people who I am very grateful for. I would like to express my immense gratitude to my research advisor, Professor Zhu Chunxiang whose guidance, stimulating suggestions and encouragement have helped me tremendously in my research throughout the years in the Ph.D candidature and in the writing of this thesis. Professor Zhu shared with me his knowledge not only on the academic field but also on life skills, for which I am very thankful. I would also like to thank Professor Yeo Yee Chia, Dr. Philipp Steinmann, Dr. Rick Wise and Dr. Ming-Bin Yu for the meaningful discussions on the topics presented in this thesis. I especially thank Dr. Steinmann for his recommendation of the journal articles which were very useful and relevant. I am grateful to be part of the Silicon Nano Device Lab (SNDL) which was well taken care of by Mr. Yong Yu Fu, Mr. O Yan Wai Linn, Mr. Patrick Tang and Mr. Lau Boon Teck. I specifically appreciate Mr. O Yan’s help in troubleshooting and maintenance of the equipments under my charge. I would like to thank my friends and seniors, specifically Dr. Xie Ruilong, Dr. Chen Jingde, Mr. Sun Zhiqiang and Mr. Dharani Kumar Srinivasan for their useful discussions and assistance. My deepest gratitude goes to my family whose support gave me strength to overcome numerous obstacles during the study. Last but not least, a special thank to my dear Hai Ha, for your love and encouragement. i Table of Contents Acknowledgements . i Abstract . iv List of figures vi List of tables . xii List of abbreviations and symbols xiii Chapter 1: Introduction . 1.1. Radio Frequency and Analog/Mixed-Signal Technology 1.2. MIM capacitors in the RF and AMS circuits 1.3. Motivation of the thesis 1.4. Thesis outline and contributions References Chapter 2: Literature and Technology Review . 2.1. Requirements of an MIM capacitor for RF and AMS integrated circuits 2.2. High-k dielectrics 13 2.2.1 Binary metal oxide 14 2.2.2 Ternary metal oxide 16 2.2.3 Stacked dielectrics 20 2.3. Other parameters affecting the performance of the MIM capacitors 23 2.4. Summary 26 References 28 Chapter 3: Silicon Dioxide (SiO2) for MIM Applications . 36 3.1. Introduction 36 3.2. MIM capacitors with PECVD SiO2 37 3.2.1 Experiments 37 3.2.2 Results and Discussion 38 3.3. MIM capacitors with ALD SiO2 42 3.3.1 Experiment 42 3.3.2 Results and discussion 43 3.3.3 Performance comparison of ALD and PECVD SiO 54 3.4. Modeling of the negative quadratic VCC of SiO2 55 3.5. Summary 63 References 64 ii Chapter 4: High Performance MIM Capacitors with Er2O3 on ALD SiO2 . 69 4.1. Introduction 69 4.2. Single layer Er2O3 MIM capacitor 70 4.3. High performance MIM capacitors with Er 2O3 on ALD SiO2 77 4.3.1 Effect of substrate plasma on the performance of the MIM capacitors 78 4.3.2 Er2O3/SiO2 MIM capacitor 81 4.4. Summary 94 References 96 Chapter 5: MIM Capacitors for High Voltage Applications 101 5.1. Introduction 101 5.2. .. .Capacitors and Dielectrics Both capacitors shown here were initially uncharged before being connected to a battery They now have separated charges of +Q and – Q on their two... Change the voltage and see charges built up on the plates Observe the electric field in the capacitor Measure the voltage and the electric field Capacitor Lab 11/14 Capacitors and Dielectrics Section... plastic, depending upon purpose and size Insulating materials, called dielectrics, are commonly used in their construction, as discussed below Some typical capacitors Size and value of capacitance are