- Titel
- Organic Permeable Base Transistors: Reliable large-scale fabrication for high-frequency devices and memories
- Zitierfähige Url:
- https://nbn-resolving.org/urn:nbn:de:bsz:14-qucosa2-1060332
- Erstveröffentlichung
- 2026
- Datum der Einreichung
- 12.09.2025
- Datum der Verteidigung
- 17.03.2026
- Abstract (EN)
- Organic materials have demonstrated their ability to complement, rather than replace, silicon by filling niches where their unique properties matter most. Their advantages are well known: molecular tunability, intrinsic flexibility, low-temperature processing, compatibility with solution processing and printing, and low cost. In particular, organic permeable base transistors (OPBTs) are attractive due to their vertical architecture, yielding short-channel lengths and high current densities. They have shown impressive performance and potential in various applications, such as display driving circuits, light-emitting transistors, and logic circuits requiring high-frequency operation. However, large-scale implementation is hindered by fabrication reliability and repeatability issues, a problem also common with other types of organic transistors, leading to reliance on exceptional “hero” devices. Furthermore, research is still lagging in finding an organic non-volatile memory (ONVM) which could support organic circuits with built-in memory. Thus, the outcome of this work is two-fold: To address the reproducibility challenge, an electrochemical anodization process is scaled up and optimized for OPBTs to produce consistent performance across an entire 15 cm × 15 cm wafer. The causes of failure are identified, investigated, and suppressed. By controlling the Al base oxidation, an 87% yield of functional devices and a median transconductance of 1 × 10⁻³ S is achieved, proving that the anodization can be a robust, non-destructive process. Leakage current is consistently reduced to below 1 × 10⁻⁹ A, increasing the current gain to a median of 1 × 10⁶. In addition to reducing variability, this process decreases the oxide capacitance (Cox) while minimally impacting the transconductance (gm), resulting in a driving-voltage-normalized unity-gain cutoff frequency (fT/V) of up to 2.6 MHz V⁻¹. The influence of the process on the base morphology, base sub-circuit, and device performance is studied and supported through properly calibrated technology computer-aided design (TCAD) simulations. In order to take advantage of the intrinsic speed and low operation voltages, an OPBT with an embedded floating base (FB) is introduced with the goal of producing an ONVM. Memory behavior is observed, and parameters such as FB thickness, FB area, annealing, and shelf life are investigated. Correspondingly, a proposed mechanism attributes the effect to distributed charge trapping at the control base, while the influence of the floating base is minimal due to its impermeability. Programming/erasing (P/E) conditions are defined, demonstrating multi-level operation with limited electrical erasing. Retention indicates a detrapping time constant of τ ≈ 4.1 × 10⁴ s, or approximately 1.1 h, while light-assisted erasing is demonstrated.
- Freie Schlagwörter (EN)
- Organic semiconductors, Vertical transistor, Anodization, Permeable Base, Memory, OPBT, High-frequency
- Klassifikation (DDC)
- 540
- Klassifikation (RVK)
- VN 6057
- GutachterIn
- Prof. Dr. Karl Leo
- PD. Dr. habil. Hans Kleemann
- Prof. Dr. Björn Lüssem
- BetreuerIn Hochschule / Universität
- Prof. Dr. Karl Leo
- PD. Dr. habil. Hans Kleemann
- Den akademischen Grad verleihende / prüfende Institution
- Technische Universität Dresden, Dresden
- Sonstige beteiligte Institution
- Universität Bremen, Bremen
- Version / Begutachtungsstatus
- publizierte Version / Verlagsversion
- URN Qucosa
- urn:nbn:de:bsz:14-qucosa2-1060332
- Veröffentlichungsdatum Qucosa
- 21.07.2026
- Dokumenttyp
- Dissertation
- Sprache des Dokumentes
- Englisch
- Lizenz / Rechtehinweis
CC BY-NC 4.0- Inhaltsverzeichnis
TABLE OF CONTENTS Abstract — V Zusammenfassung — VI Scientific Contributions — VII Symbols and Acronyms — XIII 1. Introduction — 1 1.1 Motivation — 1 1.2 Goal — 4 1.3 Structure of the work — 5 2. Basics — 7 2.1 From Molecules to Transport — 7 2.1.1 Organic Molecules in a Solid — 7 2.1.2 Charge Transfer Mechanisms — 10 2.1.3 Charge Transport — 13 2.2 Conduction in Organic Semiconductors and Devices — 19 2.2.1 Doping — 19 2.2.2 Space Charge Limited Conduction — 24 2.3 Injection from Contacts — 25 2.3.1 Ideal Schottky Barrier — 25 2.3.2 Image-Force Barrier Lowering — 28 2.3.3 Charge Injection Processes — 29 2.3.4 Optimizing Charge Injection — 31 2.4 Organic Field-Effect Transistors — 33 2.4.1 Principles and Advances — 33 2.4.2 Characteristics — 36 2.4.3 Challenges — 42 2.5 Organic Permeable Base Transistors — 44 2.5.1 Structure — 44 2.5.2 Permeable Base, Vertical Transport and SCLC: Previous Research and Developments — 45 2.5.3 Characteristics — 50 2.5.4 Optimization Strategies — 54 2.5.5 Parameters and Figures of Merit — 56 3. Methods and Implementation — 59 3.1 Fabrication and Processing — 59 3.1.1 Thermal Vapor Deposition — 59 3.1.2 Sample Processing — 61 3.1.3 Electrochemical Anodization — 62 3.2 Characterization Methods — 68 3.2.1 Current-Voltage Measurements — 68 3.2.2 Impedance Spectroscopy — 69 3.2.3 Small-Signal Measurements — 71 3.3 Materials — 72 3.3.1 C60 — 72 3.3.2 Aluminum Oxide — 74 3.3.3 Materials Summary — 76 4. Large-Scale Anodization of OPBTs — 77 4.1 Motivation — 77 4.2 Device Structure and Deposition — 79 4.3 Anodization Process Optimization — 81 4.3.1 Delamination and Contamination — 81 4.3.2 Anodization Conditions — 86 4.4 Anodization-Induced Blistering — 90 4.4.1 Gas Blistering — 90 4.4.2 Base Morphology and Mechanical Blistering — 93 4.5 Statistical Analysis — 97 4.6 Impact on the Base Sub-Circuit — 101 4.7 High-Frequency Operation — 104 4.8 Small-Signal Simulations — 107 4.9 Summary — 109 5. Memory Effects in OPBTs — 111 5.1 Introduction — 111 5.1.1 Motivation — 111 5.1.2 Constraints — 113 5.2 Introduction of Floating-Base OPBTs — 114 5.2.1 Architecture Motivation — 114 5.2.2 Device Structure — 115 5.3 FB-OPBT Operation and Parameters’ Influence — 117 5.3.1 Floating-Base Area Variation — 118 5.3.2 Floating-Base Thickness Variation — 120 5.3.3 Annealing and Stability — 120 5.4 Mechanism of Operation — 122 5.5 Programming and Erasing Conditions — 124 5.5.1 Programming — 124 5.5.2 Influence of the Semiconductor Charge Trapping — 128 5.5.3 Erasing — 130 5.6 Retention Characteristics — 132 5.7 Photo-Effect and Hole Trapping — 133 5.8 Summary — 136 6. Conclusion and Outlook — 139 6.1 Conclusion — 139 6.2 Outlook — 142 Acknowledgements — 179