Roadmap of Ferroelectric Memories: From Discovery to 3D Inte- gration Sourav De Maximilian Lederer Franz M¨ uller Yannick Raffel David Lehninger Ayse S¨ unb¨ ul Stefan D¨ unkel Tarek Ali Halid Mulaosmanovic Md. Aftab Baig Bhaswar Chakrabarti Sven Beyer Tian-Li Wu Johannes M¨ uller Darsen D. Lu Konrad Seidel Thomas K¨ ampfe Dr. Sourav De, Dr. Maximilian Lederer, Franz M¨ uller, Yannick Raffel, Dr. David Lehninger, Ayse S¨ unb¨ ul, Konrad Seidel, Dr. Thomas K¨ ampfe Fraunhofer IPMS-CMT, Dresden, Germany Email Address: sourav.de@ipms.fraunhofer.de, maximilian.lederer@ipms.fraunhofer.de Dr. Tarek Ali, Dr. Halid Mulaosmanovic, Dr. Sven Beyer, Dr. Johannes M¨ uller GlobalFoundries Dresden Module One, Dresden, Germany. Dr. Sourav De, Dr. Md. Aftab Baig, Prof. Darsen D. Lu Institute of Microelectronics, National Cheng Kung University, Tainan, Taiwan Prof. Tian-Li Wu International College of Semiconductor Technology, National Yang Ming Chiao Tung University, Taiwan Prof. Bhaswar Chakrabarti Department of Electrical Engineering, Indian Institute of Technology Madras, Madras - 600036 Keywords: FeFET, FefinFET, GAA-FET, HKMG, HfO2 The versatility of hafnium oxide-based ferroelectric memories to function as a storage class memory, a synaptic device for neuromor- phic implementation, and a device capable of high-density integration have made them attractive candidates for next-generation technology. Ferroelectric memories have been increasingly popular with the discovery of ferroelectricity in hafnium oxide at a shal- low thickness and compatibility with complementary metal-oxide-semiconductor-compatible processes. The single transistor-based ferroelectric cell makes them ideal for non-volatile embedded memory solutions, bridging the gap between on-chip SRAM and exter- nal data storage (e.g. Flash). This paper begins with discovering ferroelectricity in Rochelle salt and discusses the neoteric progress to successful integration with 3D memory. 1 Introduction and Brief History of Ferroelectricity The phenomenon of ferroelectric hysteresis was first observed by the Ph.D. student Joseph Valasek in 1921, who noticed the loops in the induced dielectric polarization upon applied electric fields in Rochelle salt/ C 4 H 4 KNaO 6 . This material was also known under the name Seignette salt as being first synthe- sized in the 17 th century by Pierre Seignette in La Rochelle, France from wine [1, 2]. Valasek was inves- tigating these materials for detecting earthquakes using piezoelectricity, a known phenomenon. However, this discovery went largely unrecognized at the time. For almost 15 years, ferroelectricity was considered a particular property in Rochelle salt, e.g., when Vi- taly Ginzburg looked into this effect in more detail from a theoretical solid-state physics point of view, he still coined it Seignetteoelectric. This was only until Busch and Scherrer discovered ferroelectricity in potassium dihydrogen phosphate/KH 2 PO 4 (KDP) in 1935. However, the hysteretic behavior showed similarities to the conduct of the magnetization upon an external magnetic field found some decades ear- lier by Alfred Ewing in iron (lat. ferrum), hence coined ferromagnetism [3]. Due to these similarities, the effect later got its name, ferroelectricity, even though iron is not the physical root cause of the impact. During World War II, the anomalous dielectric properties of barium titanate/BaTiO 3 (BTO) were dis- covered in ceramic specimens, independently by Wainer and Solomon in the USA, by Ogawa in Japan, and by Wul and Goldman in the Soviet Union [4, 5, 6, 7]. Unlike Rochelle salt, BTO and KDP are in- soluble in water, chemically stable at room temperature, and have much better electrical and mechanical properties. 1