ABSTRAK Telah dilakukan fabrikasi dan karakterisasi lapisan tipis Barium Strontium Titanat Ba0.5Sr0.5TiO3 (BST) dengan metode sol gel. Penelitian ini bertujuan untuk menganalisa pengaruh temperatur annealing terhadap struktur mikro lapisan tipis BST yang ditumbuhkan dengan metode sol gel spin coating. Pada penelitian ini, lapisan tipis BST dideposisi diatas substrat gelas preparat dengan metode sol gel teknik spin coating. Preparasi larutan BST dilakukan dengan melarutkan titanium dioksida TiO2, dilarutkan dengan etilen glikol (HOCH2CH2OH) kemudian ditambahkan asam citrit C6H8O7 lalu ditambahkan barium karbonat BaCO3, strontium karbonat SrCO3, dan diaduk dengan menggunakan hotplate magnetic stirrer. Selanjutnya ditambahkan. Proses deposisi dilakukan dengan cara meneteskan larutan BST di atas substrat yang diletakkan di atas holder pada alat spiner, dan diputar dengan kecepatan 3000 rpm selama 30 detik. Lapisan tipis BST yang terbentuk selanjutnya dianil pada variasi temperatur 500oC, 550oC, 600oC, 650oC, dan 700oC, dengan waktu penahanan 15 jam. Struktur dan morfologi permukaan lapisan tipis BST yang terbentuk selanjutnya dianalisa dengan menggunakan XRD dan AFM. Hasil penelitian menunjukkan bahwa lapisan yang di anil pada temperatur 700oC menghasilkan fasa tunggal Ba0.5Sr0.5TiO3. Temperatur anil yang semakin tinggi cenderung menghasilkan kristal BST dengan ukuran butir yang lebih besar. Pengujian dengan AFM meperlihatkan bahwa lapisan yang dianil pada temperatur 500oC dan 600oC memiliki permukaan yang lebih rata dan ukuran granula yang cenderung seragam. Kata kunci : Lapisan tipis BST, spin coating, temperatur anil, struktur mikro. ABSTRACT The preparation and characterization of Barium Strontium Titanate Ba0.5Sr0.5TiO3 (BST) thin films had been done using sol gel methods. In this study, a BST is a ferroelectric material and has a promising apllication especially in the new generation of electronic devices. This aims of this research is to analyze the effect of annealing temperature on the microstructure of the BST thin film grown by sol gel spin coating method. In this study, a BST thin films was deposited on the glass substrate and prepared by sol-gel spin coating technique. The solution was prepared by dissolving the titanium dioxide TiO2, reconstituted with etilen glycol (HOCH2CH2OH) and then acid citric C6H8O7 ware and added barium carbonate BaCO3, strontium carbonate SrCO3, and stirred using a hotplate magnetic stirrer. Deposition process was done by dropping the BST solution on to glass substrate, placed on substrate holder of the spinner apparatus and rotated with speed of 3000 rpm for 30 seconds. Then, the BST thin films which had been formed, subsequently annealed at 500oC- 700oC for 15 hours. Structure and the surface morphology of BST thin films analyzed using XRD and AFM. The results showed that the films annealed at temperature of 700°C has single phase Ba0.5Sr0.5TiO3. High annealing temperature tends to produce crystalline BST with larger grain size. Testing with AFM showed that the filmannealed at temperatures of 500oC and 600oC have a more flat surfaces and uniform size of granules are likely Keywords: BST thin films, spin coating, annealing temperature, microstructure. ABSTRACT The preparation and characterization of Barium Strontium Titanate Ba0.5Sr0.5TiO3 (BST) thin films had been done using sol gel methods. In this study, a BST is a ferroelectric material and has a promising apllication especially in the new generation of electronic devices. This aims of this research is to analyze the effect of annealing temperature on the microstructure of the BST thin film grown by sol gel spin coating method. In this study, a BST thin films was deposited on the glass substrate and prepared by sol-gel spin coating technique. The solution was prepared by dissolving the titanium dioxide TiO2, reconstituted with etilen glycol (HOCH2CH2OH) and then acid citric C6H8O7 ware and added barium carbonate BaCO3, strontium carbonate SrCO3, and stirred using a hotplate magnetic stirrer. Deposition process was done by dropping the BST solution on to glass substrate, placed on substrate holder of the spinner apparatus and rotated with speed of 3000 rpm for 30 seconds. Then, the BST thin films which had been formed, subsequently annealed at 500oC- 700oC for 15 hours. Structure and the surface morphology of BST thin films analyzed using XRD and AFM. The results showed that the films annealed at temperature of 700°C has single phase Ba0.5Sr0.5TiO3. High annealing temperature tends to produce crystalline BST with larger grain size. Testing with AFM showed that the filmannealed at temperatures of 500oC and 600oC have a more flat surfaces and uniform size of granules are likely Keywords: BST thin films, spin coating, annealing temperature, microstructure.