DOI: 10.1007/s00339-006-3494-3 Appl. Phys. A 83, 285–288 (2006) Materials Science & Processing Applied Physics A s. halder 1, ✉ p. gerber 1 t. schneller 1 r. waser 1,2 Structural, dielectric and electromechanical study of Hf-substituted BaTiO 3 thin films fabricated by CSD 1 Institut fuer Werkstoffe der Elektrotechnik, RWTH Aachen, Aachen 52056, Germany 2 CNI, Forschungszentrum Juelich, Juelich 52425, Germany Received: 10 November 2005/Accepted: 9 January 2006 Published online: 8 February 2006 • © Springer-Verlag 2006 ABSTRACT Hafnium-substituted barium titanate thin films were deposited on platinized silicon substrates. Two differ- ent concentrations of solutions (0.1M and 0.3 M) were used to deposit films of various compositions Ba(Ti 1−x , Hf x )O 3 (x = 0.03, 0.05, 0.07, 0.1, 0.2, 0.3 and 0.4). The microstruc- ture of the films depended on the concentration of the solution. Lower concentration (0.1 M) solutions led to columnar films, but with higher hafnium percent compositions the columnar structure was lost. The films which were derived from the 0.1M concentration solutions had better dielectric and electrical prop- erties compared to the films derived from a higher concentration (0.3 M). All the films were found to be polycrystalline in nature. The dielectric constant of the films was found to decrease with higher amounts of hafnium substitution. From the I –V charac- teristics it is noticed that the leakage decreases by almost four orders of magnitude with a hafnium substitution of 40%. The d 33 values of the films were between 23 and 5.6 pm/V for the different films. PACS 68.55.-a; 81.20.Fw; 77.84.Dy; 77.55.+f 1 Introduction Thin films of complex oxides possess a wide range of electrical and optical properties and hence their integration with silicon is highly desirable. Their role is as varied as in applications like metal insulator metal capacitors, integrated micro-electromechanical systems (MEMS) and metal ferro- electric semiconductor field effect transistors (MFSFETs). Various methods have been used to deposit complex oxides, like metal organic chemical vapor deposition (MOCVD) [1], pulsed laser deposition (PLD) [2], sputtering [3] and chemical solution deposition (CSD) [4]. Substituted barium titanate thin films have been attracting a lot of attention recently because of their potential application in high-density capacitors, tunable microwave devices, etc. The A-site-substituted barium strontium titanate (BST) thin films have gained the most attention amongst them. Among the B-site substitutions most attention has been paid to zir- conium (Zr) substitution due to its electromechanical proper- ✉ Fax: +49-241-8022300, E-mail: halder@iwe.rwth-aachen.de ties [5]. Simultaneously there has been a growing emphasis on hafnium oxide over zirconium oxide based gate dielectrics due to its better leakage properties, lower reactivity with gate electrodes and larger conduction-band offset to silicon [6, 7]. Recent reports on the substitution of Hf in lead titanate thin films show that it has better fatigue and imprint properties [8]. Consequently, it is of great interest to see the effect of Hf sub- stitution in barium titanate thin films for capacitors. This work deals with the effect of Hf substitution on the dielectric and electromechanical properties of Hf-substituted thin films. 2 Experimental Thin films of Ba(Ti 1−x , Hf x )O 3 were deposited by chemical solution deposition (CSD) on Pt/TiO 2 /SiO 2 /Si substrates. The starting materials for the preparation of the so- lution were barium propionate, hafnium tetra-n-butoxide and titanium tetra-n-butoxide. Ba(Ti 1−x , Hf x )O 3 precursor solu- tions with x = 0.03, 0.05, 0.07, 0.1, 0.2, 0.3 and 0.4 were syn- thesized. For each composition solutions of 0.1M and 0.3M concentrations were synthesized. They will be henceforth re- ferred to as BHT3, BHT5, BHT7, BHT10, BHT20, BHT30 and BHT40. Before the solution was deposited, the substrates were an- nealed for a few minutes at 700 ◦ C to reduce any residual mechanical stress. The substrates were each 1 square inch in size. After the solution was deposited it was first spun at 500 rpm for 5s and then at 4000 rpm for 30 s. Then the films were annealed at 700 celsius for 15 min. The desired thickness (approximately 390 nm, measured with a DEK- TAK surface profilometer) was achieved after 40 coatings for the 0.1M solutions and 12 coatings for the 0.3M solu- tions. All the films were finally annealed for 30 min. Platinum electrodes were structured on the top surface with a pho- tolithographic lift−off process. After deposition of the top electrodes the films were once again annealed for 5 min to establish better contact between the top electrodes and the surface. Temperature-dependent dielectric studies were per- formed using an impedance analyzer (HP4294A). I –V meas- urements were performed with a Keithley 617 programmable electrometer. For electromechanical measurements, the backsides of the samples were polished and Au coated by vapor deposition for