Pulsed Laser Deposition of ZnO Thin Films for Piezoelectric Applications
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Abstract Transparent, insulating ZnO thin films have been deposited in-situ by pulsed laser deposition (PLD) from sintered targets. Films were deposited on substrates of fused quartz, A12 0 3, polycrystalline and textured (111) Au, at several substrate deposition temperatures (TSubstraIe - 7000 C) and background oxygen pressures (P 3000
Good
11
Good
0
0
300
2000
6 +poly
25
200
10000
80
50
200
11000
3.60
> 10000
Poor
0, 50
24, 400
2000, 8000
4.80
54
Good
0
76 to 210 @ 0.2/s
10000
80
Cr 0 Au 43
100 228
Poor
Good
2.60 4000 8000 Table 1: Pulsed Laser Deposition of Gold
Poor
techniques included PLD, IBAD, and sputtering. Typically, the deposited Au films were (111) textured with the degree of alignment dependent on the technique and the deposition conditions. The quality of the deposited film was determined from the 'F(111) and the ratio of the intensities of the (111) and (002) reflections. The best aligned films had values of F(1 11) from 2-3o with no measurable (002) intensity. Films were also tested for adhesion. In general, the more adherent films displayed the widest F(Au,11). In Table I are listed some typical PLD results. PLD gold films deposited in vacuum typically adhered well to the Si substrate, but were poly-crystalline (F(Au,111)=7-10'). Different pressures of Argon (2550 mTorr) were added to vary the kinetics of the arriving photo-ablated species onto the substrate. A narrower F(Au,111) of 3.6' was obtained with 50 mTorr Ar pressure and 20 00 C; the film did not adhere. One film was deposited with a thin Au seed layer Tsubstrate= in vacuum (for good adhesion) followed by a thicker Au layer in 50 mTorr of Ar at 40 00 Tsubstrate= C; it displayed good adhesion and a F(Au,111) >4.8'. A film deposited with
a thin Cr seed layer at 1000 C followed by a thicker Au layer (43 mTorr Ar, 2280 C) had a F(Au,lll) of 2.6° but the film did not adhere. The surfaces of most metallizations were rough, as shown by the SEM micrograph (Figure 1A.) Deposition of gold with IBAD and by evaporation, with and without a chromium layer, was also attempted, with results summarized in Table II. Again, there was a negative correlation between alignment and adhesion. We have been unable to duplicate published results on RF-sputtered ZnO on evaporated Au on Cr on fused quartz for Au quality and Table II: IBAD Metallization Layers Ion Species
Energy, eV
TsUBSTRATE
F(Au, 111)
Adhesion
O
100
100
Good
Ar
100
100
Poor
Ar
700
< 100 OC
60
Poor
O+Ar(25 nm) then Ar
200
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