Table 1.

The recent developed SMO thin film based resistance hydrogen sensors.

Materials	Synthesis Method	Working Temp. (°C)	Detected Conc. (ppm)	Hydrogen response				Ref.
				Smax	Conc. (ppm)	tresponse	Temp. (°C)
SnO2	Sol-gel annealing	100–300	50–5,000	104	5,000	<10 s	100	[65]
In2O3 doped SnO2	Sol-gel annealing	22	100–15,000	105	15,000	tens of min.	22	[83]
(101)-SnO2	RF magnetron sputtering	550	300–10,000	300	10,000	<16 s	550	[70]
SWCNT doped SnO2	Sol-gel annealing	150–300	300–1,500	3	1,500	<5 s	250	[80]
Au or Pt enhanced SnO2	Sol-gel annealing	85–180	500–10,000	2	10,000	several min.	150	[79]
SnO2	Spray pyrolysis	250–400	1,000	3,040	1,000	2 s	350	[121]
Pd doped SnO2	Reactive Magnetron sputtering	50–300	10–1,000	85	1,000	several mins	200	[60]
SnO2	Sol-gel annealing	90–220	1,000	2,000	1,000	15 s	150	[66]
Al-doped ZnO	HF magnetron sputtering	40–100	1,000–5,000	10	1,000	10 min	100	[76]
ZnO wirelike thin film	Thermal oxidation	200	200	2.83	200	1.5 min	200	[68]
ZnO	Thermal oxidation	400	40–160	4,000	160	1,000 s	400	[122]
Mg-doped ZnO	PLD	150–300	5–5,000	50	5,000	5 min	300	[77]
Nanoporous TiO2	Thermal oxidation	500	5–500	10	500	10 s	500	[11]
Nanoporous TiO2	Anodic oxidation	100–300	1,200–10,000	1.24	10,000	-	225	[67]
Anatase TiO2	Micro-arc oxidation	100–300	1000	2.5	1,000	45 s	250	[71]
Nb2O5 NW thin film	Thermal oxidation	20	100–2,000	50	2,000	<2 min	20	[69]
MWCNT-doped WO3	Electron beam evaporation	200–400	100–50,000	3	1,000	-	350	[81]
Pd-doped WO3	Sol-gel annealing	20–350	1,000–1,300	104	1,000	<100 s	20	[78]
Pt-doped WO3	RF magnetron sputtering	95–220	30–200	9.5	200	0.7 min	200	[123]
CuO	Thermal oxidation	300–800	60,000	3.72	60,000	5 min	250	[72]
NiO	PLD	25–250	30,000	1.16 (n) 1.76 (p)	30,000	10 min	125	[124]
NiO	Magnetron sputtering	300–650	500–10,000	190 (p)	5,000	5 min	400	[74]