AIST Stories No1
9/36

Leading the way AIST!7at a glanceTerminologyMR ratio of 150% at room temperature, was highly praised and he won a research grant.He investigated a number of ways to achieve very high MR ratios, and diligently pursued the research by himself. One of the ways he considered was using crystalline magnesium oxide (MgO).“This method was theoretically posited by researchers in the US and Europe in 2001, but experiments did not go well so it was almost abandoned. However, I felt it had potential and I decided to take a chance on magnesium oxide crystal.”The first year on Sakigake funded the construction of an apparatus for thin film deposition and ended without producing any results. The apparatus was not finished until near the end of 2003.“When I finally completed it, I rushed to start my experiments. The first MTJ samples I produced went straight to an MR ratio of 88% at room temperature, which was the highest value in the world at the time. At only the third try, the MR ratio reached 180%. I was amazed by this virtually instant success.”At the time, he had a feeling that magnesium oxide was a material with “an excellent nature.” In fact, as the research has progressed, the MR ratio has reached 600%.Thanks to collaboration with industry, a smooth path through “the valley of death” of developmentNow his basic research had provided magnificent results, but he had only been producing MTJ films on small, specialized substrates, at a rate of one per day. There was still a huge barrier to overcome for industrial application: developing the technology for mass production.“My MTJs using magnesium oxide have a crystal structure with four-fold rotational symmetry in a film plane. However, for use in an HDD head or a non-volatile memory, the crystal structure must be grown on a base structure that has three-fold rotational symmetry in a film plane. Everybody knew that this is impossible.” For comparison, this is like having to pile marbles in a square pattern on top of other marbles arranged in a triangular pattern. However, a researcher is not the kind of person to accept that something is impossible just because it is unknown.With the goal of mass production, he started collaborative A history of magnetoresistance effect discoveries and its industrial applicationsmaterial that is not regular and is not a crystalline structure.*8 Sakigake (PRESTO): A program run by the JST to promote goal-oriented basic research directed toward strategic objectives set by the government of Japan. It is focused on individual research, to cultivate the seeds of future innovation.Tunnel magnetoresistance effect/TMR effectA phenomenon in which a tiny tunnel current flows through an insulator layer when a voltage is applied to the two sides of a magnetic tunnel junction, and the resistance value (how easily this current flows) changes in accordance with magnetic fields. In general, the resistance is lower when the magnetizations of the ferromagnetic layers are parallel in the same direction and the resistance is higher when the magnetizations are parallel but opposite (anti-parallel).eeeeeeMR ratio = (RAP-RP) / RP×100% (a performance index)Parallel magnetizations (P)Ferromagnetic metal layerFerromagnetic metal layerTunnel resistance RP: LowAnti-parallel magnetizations (AP)Tunnel resistance RAP: HighInsulator layer (nanometer thickness)(tunnel barrier)Magnetoresistanceeffects and MR ratiosIndustrialapplicationsYear1857Even larger MR ratios will be necessaryto developnext-generation deviceswith higher performance andlower power consumption.HDD headsNon-volatilememories198519901995200020052010Inductive headsMR headsGMR headsTMR headsMRAMAMR MR=1−2%GMRMR=5−15%TMR (Al–O)MR=20−70%Leading the way AIST!7at a glanceTerminologyMR ratio of 150% at room temperature, was highly praised and he won a research grant.He investigated a number of ways to achieve very high MR ratios, and diligently pursued the research by himself. One of the ways he considered was using crystalline magnesium oxide (MgO).“This method was theoretically posited by researchers in the US and Europe in 2001, but experiments did not go well so it was almost abandoned. However, I felt it had potential and I decided to take a chance on magnesium oxide crystal.”The first year on Sakigake funded the construction of an apparatus for thin film deposition and ended without producing any results. The apparatus was not finished until near the end of 2003.“When I finally completed it, I rushed to start my experiments. The first MTJ samples I produced went straight to an MR ratio of 88% at room temperature, which was the highest value in the world at the time. At only the third try, the MR ratio reached 180%. I was amazed by this virtually instant success.”At the time, he had a feeling that magnesium oxide was a material with “an excellent nature.” In fact, as the research has progressed, the MR ratio has reached 600%.Thanks to collaboration with industry, a smooth path through “the valley of death” of developmentNow his basic research had provided magnificent results, but he had only been producing MTJ films on small, specialized substrates, at a rate of one per day. There was still a huge barrier to overcome for industrial application: developing the technology for mass production.“My MTJs using magnesium oxide have a crystal structure with four-fold rotational symmetry in a film plane. However, for use in an HDD head or a non-volatile memory, the crystal structure must be grown on a base structure that has three-fold rotational symmetry in a film plane. Everybody knew that this is impossible.” For comparison, this is like having to pile marbles in a square pattern on top of other marbles arranged in a triangular pattern. However, a researcher is not the kind of person to accept that something is impossible just because it is unknown.With the goal of mass production, he started collaborative A history of magnetoresistance effect discoveries and its industrial applicationsmaterial that is not regular and is not a crystalline structure.*8 Sakigake (PRESTO): A program run by the JST to promote goal-oriented basic research directed toward strategic objectives set by the government of Japan. It is focused on individual research, to cultivate the seeds of future innovation.Tunnel magnetoresistance effect/TMR effectA phenomenon in which a tiny tunnel current flows through an insulator layer when a voltage is applied to the two sides of a magnetic tunnel junction, and the resistance value (how easily this current flows) changes in accordance with magnetic fields. In general, the resistance is lower when the magnetizations of the ferromagnetic layers are parallel in the same direction and the resistance is higher when the magnetizations are parallel but opposite (anti-parallel).eeeeeeMR ratio = (RAP-RP) / RP×100% (a performance index)Parallel magnetizations (P)Ferromagnetic metal layerFerromagnetic metal layerTunnel resistance RP: LowAnti-parallel magnetizations (AP)Tunnel resistance RAP: HighInsulator layer (nanometer thickness)(tunnel barrier)Magnetoresistanceeffects and MR ratiosIndustrialapplicationsYear1857Even larger MR ratios will be necessaryto developnext-generation deviceswith higher performance andlower power consumption.HDD headsNon-volatilememories198519901995200020052010Inductive headsMR headsGMR headsTMR headsMRAMAMR MR=1−2%GMRMR=5−15%TMR (Al–O)MR=20−70%

元のページ 

10秒後に元のページに移動します

※このページを正しく表示するにはFlashPlayer9以上が必要です