Semiconducting TiO2 for High Performance Ferroelectric Tunnel Junctions

• Main Author: Wikare, Erik
• Format: Other/Unknown Material
• Language: English
• Published: Lunds universitet/Institutionen för elektro- och informationsteknik 2022
• Subjects: Technology and Engineering; Nordpol*
• Online Access: http://lup.lub.lu.se/student-papers/record/9093738

The ferroelectric tunnel junction FTJ is a rather old concept but has recently been in the spotlight for its promising properties in computer memory technology and neuromorphic computing. The device consists of a ferroelectric insulator sandwiched between two electrodes, and by polarisation switching the resistance along the heterostructure can drastically be adjusted. The optimisation possibilities of the FTJ are extensive as new materials and processing methods are constantly being discovered. In this thesis, FTJ components will be processed, and an interfacial layer of TiO2 will be deposited using plasma-enhanced atomic layer deposition between a ferroelectric hafnium zirconate (HZO) layer and electrode to investigate its effect on the performance. Here, the ALD deposition conditions will be altered as well as the TiO2 layer thickness and placement in the heterostructure. Firstly, the TiO2 deposition technique will be studied to help understand the impact of the TiO2 layer. Several FTJs were fabricated and characterised. The highest remnant polarisation displayed in this thesis was 13.52 mu C/cm with an asymmetric coercive field of -1.7 and 0.9 MV/cm. The TER of the FTJ was 2.9. However, the tool used for HZO deposition was not working correctly during this thesis, but qualitative conclusions could still be made. Ferroelektricitet upptäcktes först 1921 av professorn Joseph Valasek i kaliumnatriumtartrat, ett ämne som är mer känt som "Rochelle salt". Valasek beskrev likheten mellan ferroelektricitet och det redan då väl beskrivna ferromagnetismen. Likt ferromagnetiska material och deras permanenta magnetiska poler uppvisar ferroelektiska material en permanent elektrisk polarisation, en separation av laddningar. På samma sätt som en magnet har en syd- och nordpol, har ferroelektiska material en positiv och en negativ elektriskt laddad pol. Valasek lyckades definiera karakteristiken hos ferroelektriska material långt innan man upptäckte nyttan av dem. Sedan dess har ferroelektriska material funnit sin väg in ...