Browse Prior Art Database

IrMn Bottom Spin Valves With Improved Signal Using Si Underlayers

IP.com Disclosure Number: IPCOM000013487D
Original Publication Date: 2002-May-03
Included in the Prior Art Database: 2003-Jun-18
Document File: 3 page(s) / 109K

Publishing Venue

IBM

Abstract

Disclosed is the application of Silicon (Si) underlayers for use in spin valves. Si underlayers increase the ∆ R/R from 7.1% to 8.8% in top IrMn spin valves, and 6% to 7.8% for bottom IrMn spin valves. This is accompanied by a decrease in sheet resistance and the exchange anisotropy field, Hex. These results suggest that films grown on Si have larger grains than those with other seed layers. Figure 1 shows data from IrMn “top” spin valves grown on Si underlayers. The structure was: t Si/40 NiFe/5 CoFe/25 Cu/30 CoFe/80 IrMn/30 Ru. With 10Å Si as an underlayer the properties are very similar to control samples with Ru as the underlayer: ∆ R/R is 7.1% and Hex is 392 Oe. For tSi>20 Å ∆ R/R is significantly higher at 8.8%. Concurrently, Hex drops to 224 Oe and the sheet resistance drops from 21.8 to 18.2 Ohm/square. This would suggest that the films grown on Si have a larger grain diameter. This would lead to lower R and higher ∆ R/R due to decreased grain boundary scattering. Also, this would explain the lower Hex. Hex typically follows a 1/a relationship where a is the average area of an antiferromagnetic grain. This is the case where NiFeCr/NiFe underlayers are used[2]. 9.0 500

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IrMn Bottom Spin Valves With Improved Signal Using Si Underlayers

  Disclosed is the application of Silicon (Si) underlayers for use in spin valves. Si underlayers increase the ∆R/R from 7.1% to 8.8% in top IrMn spin valves, and 6% to 7.8% for bottom IrMn spin valves. This is accompanied by a decrease in sheet resistance and the exchange anisotropy field, Hex. These results suggest that films grown on Si have larger grains than those with other seed layers.

Figure 1 shows data from IrMn "top" spin valves grown on Si underlayers. The structure was: t Si/40 NiFe/5 CoFe/25 Cu/30 CoFe/80 IrMn/30 Ru. With 10Å Si as an underlayer the properties are very similar to control samples with Ru as the underlayer: ∆R/R is 7.1% and Hex is 392 Oe. For tSi>20 Å ∆R/R is significantly higher at 8.8%. Concurrently, Hex drops to 224 Oe and the sheet resistance drops from 21.8 to 18.2 Ohm/square. This would suggest that the films grown on Si have a larger grain diameter. This would lead to lower R and higher ∆R/R due to decreased grain boundary scattering. Also, this would explain the lower Hex. Hex typically follows a 1/a relationship where a is the average area of an antiferromagnetic grain. This is the case where NiFeCr/NiFe underlayers are used[2].

9.0

500

(1)

400

Ex chang e Field (Oe)

Figure 1: ∆R/R (� ) and Exchange Field (▲) for IrMn spin valves with Si underlayers. Data for top spin valves with the structure t Si/40 NiFe/5 CoFe/25 Cu/30 CoFe/80 IrMn/30 Ru. Lines are guides to the eye.

Often, Cu layers are placed behind the free layer[3], as in the structure: substrate/seed/Cu/free layer/spacer/pinned-layer/AF/cap. The backing layer gives the electrons a longer path to travel

1

8.5

R/R

Hex

R/R

300

8.0

%200

7.5

100

07.00204060

Si thickness (Å)

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before being scattered at the seed layer (typically Ta or Ru) resulting in higher ∆R/R than un-backed spin valves with the same free layer moment. This is not the case where Cu is inserted into a top spin valve with a NiFeCr seed layer (e.g. NiFeCr/Cu/NiFe/Cu/Co/AF/Cap). The NiFeCr does not recrystallize into the larger grained structure when Cu is deposited directly upon it, and ∆R/R is actually lower than without the added Cu layer. In contrast, when Cu backing layers are interposed into a spin valve with a Si underlayer, the GMR is enhanced. This is shown in Fig. 2 for spin valves with the structure 30 Si/t Cu/40NiFe/5 Co/25 Cu/30 CoFe/80IrMn30 Ru. GMR increases from 8.4% to 9.4% with only 5Å of Cu as a backing layer and reaches a top value of 9.8%. Concurrently, Hex drops from 222 to 165 Oe and the sheet resistance drops from 16.6 to 15.6 Ohm/square. Some decrease in sheet resistance is expected due to the...