Bai giang thay Vu Xuan Hien VLKT

1/19/2026
Hanoi University of Science and Technology I.1. Gas Sensor ? School of Engineering Physics INTRODUCTION TO METAL OXIDE NANOMATERIALS Vu Xuan Hien I.1. History of Gas Sensor Canary in a cage
• Canaries are more susceptible than Field effect Surface acoustic wave Metal oxide Optical Electrochemical
humans to low oxygen, methane gas, or gas sensor (SAW) gas sensor gas sensor gas sensor gas sensor CO gas.
• A passed out canary means a dangerous gas situation.
Flame Safety Lamp (Davey’s Lamp)
• Invented by Sir Humphry Davey (of England) in 1815
• Oil flame adjusted to specific height in fresh air Sensor Structure
John Bardeen, William Shockley, Walter Brattain Taguchi
 Brattain and Bardeen first reported gas sensitive effects on Ge in 1953.
 Heiland, Bielanski and Seiyama found gas sensing effects on metal oxides.
 Taguchi finally brought metal oxide gas sensor to an industrial product focused of explosive gases. 1 1/19/2026 2 1/19/2026 Depletion zone Accumulation zone n-type semiconductor p-type semiconductor KNU 2015/05/21 954 Target Material Metallic Cu 952 O 3, 4, 6 % 2/(Ar+O2) 950 RF-magnetron Sputtering Power 30 W 948 200ppm ) NH3 Working Pressure 5 mTorr Air 946 (ohm Growth Temperature 550 oC 944 Base Pressure 3×10-6 Torr esistance R 942 100ppm NH3 Target-Substrate Distance 80 mm 940 938 50ppm Deposit Time 30 min NH 936 3 0 10 20 30 40 50 Separating electrode Time (minute) 1.02 150oC 200oC 1.01 Mount electrode on TO-Header (Use silver paste) 1.00 esistance 0.99 R Connect electrode to the pins by silver wires 0.98 elative (use silver paste) R 0.97 NH 3(200ppm) + Air Air
Dry in oven at 90oC for 40 minutes 0.96 0 10 20 30 40 50 60 70 80 90 Time (minute) 3 1/19/2026 1 1 1 1 = + + ⋯ + Laser 𝑅 𝑅 𝑅 𝑅 - Power: 65 mW - Blue (λ = 405 nm) - Green (λ = 510 nm) - Red (λ = 658 nm) Chamber Stainless steel Temperature: RT Humidity: ~25% Hot Plate Temperature: 25 oC
2𝑁𝐻 𝑔𝑎𝑠 + 3𝑂 → 𝑁 𝑔𝑎𝑠 + 3𝐻 𝑂 𝑔𝑎𝑠 + 6𝑒
2𝑁𝐻 𝑔𝑎𝑠 + 3𝑂 → 𝑁 𝑔𝑎𝑠 + 3𝐻 𝑂 𝑔𝑎𝑠 − 6ℎ 6E-08 On On On On S1 R 5E-08 S ) 2 4E-08 urrent(A C 3E-08 hoto P 2E-08 1E-08 20 ppm H2S Dry air -400 0 400 800 1200 1600 2000 2400 2800 Time (s) 4