Samopobuđeni terahercni oscilator temeljen na heterostrukturi dielektrik-feroelektrik

master's thesis

• Title (english): Self-excited terahertz oscillator based on dielectric-ferroelectric heterostructure
• Author: Bruno Pavlaković
• Mentor: Danko Radić (mentor)
• Committee member: Danko Radić (predsjednik povjerenstva)
• Committee member: Mario Basletić (član povjerenstva)
• Committee member: Željko Skoko (član povjerenstva)
• Committee member: Maja Planinić (član povjerenstva)
• Committee member: Zoran Rukelj (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2024-09-26, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

Već dugo poznata pojava negativnog električnog kapaciteta predstavlja način povećanja efikasnosti tranzistora, ali izvorno javlja se kao nestabilno stanje oko faznog prijelaza, odnosno granice između paraelektričnog i feroelektričnog stanja. Upravo ta nestabilnost uzrokuje pojavu histereze odnosno tromosti zakretanja spontane polarizacije feroelektrika i time onemogućuje njegovu primjenu na visokofrekventne elektroničke uređaje u praksi. Cilj ovog rada nastavlja se na prethodne napore stabilizacije područja negativnog kapaciteta feroelektričnog sloja oko kojeg se “lijepe” dielektrični slojevi u poznatu heterostrukturu, preko poznatog ponašanja feroelektrika da formira Kittelove domenske slojeve. Za takav sustav, u kojem domena polarizacije u smjeru polja raste na trošak smanjenja polarizacijske domene okrenute suprotno polju, izračunata je funkcija električne permitivnosti i uvjet dobivanja negativnog kapaciteta, razmotren je pojednostavljeni model dinamičkog režima u kojem domene i vanjsko polje opisujemo prisilnim harmoničkim oscilatorom u svrhu dobivanja okvira radnih frekvencija vanjskog polja za koje sustav stabilno oscilira. Istražena je mogućnost nastanka stabilnog graničnog kola Hopfovom bifurkacijom, tj. samopobuđenog oscilatora bez vanjskog tjeranja, u RLC krugu koji sadrži element s negativnom kapacitetom. Iznesen je zaključak provedene analize, ograničenja i potencijalne nadogradnje modela.

Abstract (english)

The well-established phenomenon of negative electrical capacitance offers a method to enhance transistor efficiency. However, it initially manifests as an unstable state near the phase transition-the boundary between paraelectric and ferroelectric states. This instability leads to hysteresis, or the inertia in rotating the spontaneous polarization of the ferroelectric, which has hindered its practical application in high-frequency electronic devices. This study builds upon previous efforts to stabilize the negative capacitance region of the ferroelectric layer. It explores dielectric layers that are incorporated into a known heterostructure, leveraging the ferroelectric’s tendency to form Kittel domain layers. For a system where the field-direction polarization domain grows at the expense of the oppositely-oriented domain, we calculated the electric permittivity function and the conditions for achieving negative capacitance. We also presented a simplified dynamic regime model, describing the domains and external field as a forced harmonic oscillator. This approach aimed to determine the range of external field operating frequencies that allow stable system oscillation. We investigated the feasibility of generating a stable limit cycle through Hopf bifurcation-specifically, a self-sustaining oscillator devoid of external excitation-within an RLC circuit incorporating an element exhibiting negative capacitance. The analysis concludes by presenting the model’s limitations and potential improvements.

• Keywords: feroelektrik; negativni električni kapacitet; Kittelovo domensko uređenje; stabilnost fiksnih točaka; granično kolo; RLC titrajni krug.
• Keywords (english): ferroelectric; negative electrical capacitance; Kittel domain arrangement; stability of fixed points; limit cycle; RLC oscillator circuit
• Language: croatian
• URN:NBN: urn:nbn:hr:217:468423
• Study programme: Title: Physics; specializations in: Education; Course: Education; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra edukacije fizike (magistar/magistra edukacije fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Embargoed access; Embargo expiration date: 2025-09-26
• Created on: 2024-11-19 11:04:20