The salient issues of integrated biosensors on a complementary metal-oxide semiconductor (CMOS) platform are the limited transducer design and the need for post-processing. To overcome these issues, a heterogeneously integrated system, which employs both CMOS and large-area processing, was proposed and developed. The system presented, could become a rapid, low-cost and disposable sensing platform for point-of-care applications. The heterogeneously integrated system, comprising a CMOS front-end circuit and disposable electrodes, was applied to measure the impedance of suspended DNA at different concentrations. The measurement showed a double sensitivity compared to the one carried out on the CMOS platform only. The noise analysis of CMOS transimpedance amplifiers was performed, and the impact of technology scaling on low-noise transimpedance amplifiers was studied using the Enz-Krummenacher-Vittoz (EKV) model. It was found that the noise performance improves slowly with device scaling down to 90 nm. Further device scaling may increase the gate leakage current noise due to the very thin gate oxide. Disposable electrodes fabricated using large-area processing are low cost and flexible in terms of design. In particular, inkjet-printed silver electrodes on glossy paper and gold electrodes on the glass substrate were characterised. Both electrodes with the same dimension agreed well in determining solution resistance. In addition, the paper-based electrodes presented an improved sensitivity of impedance measurement at low frequencies. The amorphous oxide thin-film transistor (TFT) is promising for implementing active circuits on disposable substrates. In particular, the low-frequency noise of amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs was characterised, and a TFT-based regulated cascade transimpedance amplifier was designed and simulated with the extracted device parameters. The a-IGZO TFT showed a comparable noise performance to the PMOS device in deep submicron processes. The simulated circuit featured a transimpedance gain up to 120 dB, a bandwidth of 29.4 kHz, input-referred noise PSD of 2.91 pA/√Hz, and a power consumption of 18.55 μW, indicating that TFT-based front-end circuits are promising for implementing low-cost, low-noise and low-power biosensors.

Sn (II) oxide finds numerous applications in different fields such as thin film transistors1, solar cells2 and sensors.3 In this study we present the fabrication of tin monoxide SnO by using Sn (II) ketoacid oximate complexes as precursors. Tin (II) ketoacidoximates of the type [HON=CRCOO]2Sn where R= Me 1, R= CH2Ph 2, and [(MeON=CMeCOO)3Sn]- NH4 +.2H2O 3 were synthesized by in situ formation of the ketoacid oximate ligand. The crystal structures were determined via single crystal X- ray diffraction of the complexes 1-3 revealed square planar and square pyramidal coordination environments for the Sn atom. Intramolecular hydrogen bonding is observed in all the complexes. Furthermore, the complexes were characterized by Infrared (IR), Nuclear Magnetic Resonance (NMR) and elemental analysis. From thermogravimetric analysis of 1-3, it was found that the complexes decomposed in the range of 160 – 165 oC. Analysis of the gases evolved during decomposition indicated complete loss of the oximato ligand in one step and the formation of SnO. Spin coating of 1 on silicon or glass substrate show uniform coating of SnO. Band gaps of SnO films were measured and found to be in the range of 3.0 – 3.3 eV by UV-Vis spectroscopy. X-ray photoelectron spectroscopy indicated surface oxidation of the SnO film. Heating 1 above 140 oC in air gives SnO of size ranging from 10 – 500 nm and is spherical in shape. The SnO nanomaterial is characterized by powder X-ray diffraction(XRD), Raman spectroscopy, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM).

In the last two decades, there has been considerable development for biosensor devices as the need to more efficient sensing systems is increasing for monitoring the progress of medicine and help with the early diagnosis of the pathogens and treatment of diseases that would reduce the cost of patient care. DNA sensors, in particular, have attracted attention due to their abundance of practical applications in clinical diagnoses and genetic information which increase the demand for DNA probes. On the other hand, the development of the oxide semiconductors thin film transistors (TFT) devices have been greatly increased, owing to their superior electrical properties, lower cost and large coverage areas. Building a bridge across biological elements and electronic interface using advanced (TFT) platforms are based on materials design and device architecture. Here, a solution-processed multi-layer metal oxide (TFT) is explored as a novel DNA sensor. The device engineering combines the novel hetero-structure metal oxide channel that can sustain a 2-dimensional electron gas (2DEG) which leads to a higher mobility and surface functionalization capacity to create an ultrasensitive, highly stable, and versatile DNA sensor. The prototype solid-state TFT sensor features a sub-10 nm-thick metal oxide heterojunction channel of a In2O3 and a top ZnO layer. The devices developed here rely on a pyrene-based molecule as the receptor unit that is known to intercalate into double stranded DNA with a very high-affinity constant and at very low concentration.

Carbon based semiconductors such as conjugated polymer or single walled carbon nanotubes (SWNT) are promising materials for use next generation printable and wearable electronics. Thin film transistors (TFTs) are often viewed as a building block for more complex electronic device, however, lack of proper characterization of these devices using these novel carbon-based materials is preventing their large-scale adoption. This thesis has two sections; in the first section I explored and improved a novel electrical model originally developed for organic or polymer-based TFTs called the organic virtual source emission diffusion model (OVSED). I improved this model by adding a variable contact resistance parameter and effective gate voltages. I then found better agreement between model and experimental data using this improved OVSED model against the conventional MOSFET based models: the SH and Y-function models, for poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)) based OTFTs. The new model proved to be an efficient tool for benchmarking polymer based TFTs and provided an efficient way to characterize and reduce contact resistance in the devices. In the second section, I explore the effect of light on a series of conjugated polymer wrapped SWNT TFTs. A structure property relationship was established between the wrapping polymer structure and the exposure wavelength intensity. We demonstrated that SWNT TFTs can act as photodetectors after an initial light soak. Finally, we further characterized the SWNT TFTs using our OVSED model validating the observed structure property relationship. Overall this thesis demonstrates steps towards proper characterization of emerging carbon based semiconductors used in TFTs. -- Les semi-conducteurs à base de carbone, tels que les polymères conjugués ou les nanotubes de carbone à paroi simple (SWNT), sont des matériaux prometteurs pour la prochaine génération d'appareils électroniques imprimables et portables. Les transistors à couche mince (TFT) sont souvent considérés comme un élément de base pour des dispositifs électroniques plus complexes, mais la caractérisation incorrecte de ces dispositifs utilisant ces nouveaux matériaux à base de carbone empêche leur adoption à grande échelle. Cette thèse comporte deux sections ; dans la première, j'ai exploré et amélioré un nouveau modèle électrique développé à l'origine pour les TFT organiques ou à base de polymères, appelé le modèle de diffusion d'émission de source virtuelle organique (OVSED). J'ai amélioré ce modèle en ajoutant un paramètre de résistance de contact variable et des tensions de grille effectives. J'ai ensuite constaté une meilleure concordance entre le modèle et les données expérimentales en utilisant ce modèle OVSED amélioré par rapport aux modèles conventionnels basés sur les MOSFET : les modèles à fonction SH et Y, pour les OTFT à base de poly{[N,N'-bis(2-octyldodecyl)-naphtalène-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophène)} (P(NDI2OD-T2)). Le nouveau modèle s'est avéré être un outil efficace pour comparer les TFT à base de polymères et a fourni un moyen efficace de caractériser et de réduire la résistance de contact dans les dispositifs. Dans la deuxième partie, j'explore l'effet de la lumière sur une série de TFT à base de SWNT enveloppés de polymères conjugués. Une relation structure-propriété a été établie entre la structure du polymère enveloppant et l'intensité de la longueur d'onde d'exposition. Nous avons démontré que les SWNT TFT peuvent agir comme des photodétecteurs après une imprégnation initiale de lumière. Enfin, nous avons caractérisé les SWNT TFT à l'aide de notre modèle OVSED en validant la relation structure-propriété observée. Dans l'ensemble, cette thèse démontre les étapes vers une caractérisation appropriée des semi-conducteurs émergents à base de carbone utilisés dans les TFT.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 139-143). Also available on the World Wide Web.

The focus of this thesis is the investigation of thin-film transistors (TFTs) based on amorphous oxide semiconductors (AOSs) in two circuit applications. To date, circuits implemented with AOS-based TFTs have been primarily enhancement-enhancement inverters, ring oscillators based on these inverters operating at peak frequencies up to ~400 kHz, and two-transistor one-capacitor pixel driving circuits for use with organic light-emitting diodes (OLEDS). The first application investigated herein is AC/DC rectification using two circuit configurations based on staggered bottom-gate TFTs employing indium gallium oxide (IGO) as the active channel layer; a traditional full bridge rectifier with diode-tied transistors and a cross-tied full-wave rectifier are demonstrated, which is analogous to what has been reported previously using p-type organic TFTs. Both circuit configurations are found to operate successfully up to at least 20 MHz; this is believed to be the highest reported operating frequency to date for circuits based on amorphous oxide semiconductors. Output voltages at one megahertz are 9 V and ~10.5 V, respectively, when driven with a differential 7.07 Vrms sine wave. This performance is superior to that of previously reported organic-based rectifiers. The second AOS-based TFT circuit application investigated is an enhancement-depletion (E-D) inverter based on heterogeneous channel materials. Simulation results using models based on a depletion-mode indium zinc oxide (IZO) TFT and an enhancement-mode IGO TFT result in a gain of ~15. Gains of other oxide-based inverters have been limited to less than 2; the large gain of the E-D inverter makes it well suited for digital logic applications. Deposition parameters for the IGO and IZO active layers are optimized to match the models used in simulation by fabricating TFTs on thermally oxidized silicon and patterned via shadow masks. Integrated IGO-based TFTs exhibit a similar turn-on voltage and decreased mobility compared to the shadow masked TFTs. However, the integrated IZO-based TFTs fabricated to date are found to be conductive and exhibit no gate modulation. Due to the conductive nature of the load, the fabricated E-D inverter shows no significant output voltage variation. This discrepancy in performance between the integrated and shadow-masked IZO devices is attributed to processing complications. / Graduation date: 2009

The primary objective of this thesis is to develop a process for fabricating integrated circuits based on thin-film transistors (TFTs) using zinc tin oxide (ZTO) as the channel layer. ZTO, in contrast to indium- or gallium-based amorphous oxide semiconductors (AOS), is perceived to be a more commercially viable AOS choice due to its low cost and ability to be deposited via DC reactive sputtering. In the absence of an acceptable ZTO wet etch process, a plasma-etching process using Ar/CH₄ is developed for both 1:1 and 2:1 ZTO compositions. An Ar/CH₄ plasma etch process is also designed for indium gallium oxide (IGO), indium gallium zinc oxide (IGZO), and indium tin oxide (ITO). Ar/CH₄ dry etches have excellent selectivity with respect to SiO₂, providing a route for obtaining patterned ZTO channels. A critical asset of ZTO process integration involves removing polymer deposits after ZTO etching without active layer damage. A ZTO process is developed for the fabrication of integrated circuits which use ZTO channel enhancement-mode TFTs. Such ZTO TFTs exhibit incremental and average mobilities of 23 and 18 cm²V⁻¹s⁻¹, respectively, turn-on voltages approximately 0 to 1.5 V and subthreshold swings below 0.5 V/dec when annealed in air at 400 °C for 1 hour. Several types of ZTO TFT circuits are realized for the first time. Despite large parasitic capacitances due to large gate-source and gate-drain overlaps, AC/DC rectifiers are fabricated and found to operate in the MHz range. Thus, they are usable for RFID and other equivalent-speed applications. Finally, a ZTO process for simultaneously fabricating both enhancement-mode and depletion-mode TFTs on a single substrate using a single target and anneal step is developed. This dual-channel process is used to build a high-gain two-transistor enhancement/depletion inverter. At a rail voltage of 10 V, this inverter has a gain of 10.6 V/V, the highest yet reported for an AOS-based inverter. This E/D inverter is an important new functional block which will enable the realization of more complex digital logic circuits. / Graduation date: 2009

Research on pi-conjugated organic materials in the recent past has produced enormous developments in the field of organic electronics and it is mainly due to their applications in electronic devices such as organic field effect transistors (OFETs), organic light emitting diodes (OLEDs) and organic photovoltaic cells (OPVs). The primary goal of this research work is to design and synthesize high performing charge transport organic semiconductors. One of the criteria for better performance of the organic thin film transistor (OTFT) is to have high uniform thin film morphology of the organic semiconductor layer on the substrate. The first project in this dissertation has been directed towards improving the thin film morphology of the functionalized pentacenes through liquid crystalline behaviour. The results have suggested the possibility of thermotropic liquid crystalline phases in 6,13-bis(diisopropylhexylsilylethynyl) pentacene which has no pi-stacking in its solid state and the presence of silyl group at the peri-position is crucial for the stability of the functionalized pentacenes. In the second project, i have investigated the effect of alkyl groups with varying chain length on the anthradithiophene chromophore on the performance of the charge transporting devices. Organic blend cell based on solution processable 2,8-diethyl-5,12-bis(triethylsilylethynyl) anthradithiophene has showed 1% power conversion efficiency and the performance is mainly attributed to the large crystalline phase segregation of the functionalized anthradithiophene from the amorphous soluble fullerene derivative matrix. OTFT study on alkyl substituted functionalized anthradithiophenes suggested the need of delegate balance between thin film morphology and the crystal packing. Third project has been directed towards synthesizing halogen substituted functionalized anthradithiophenes and their influence in the performance of OFETs. OTFT made of 2,8-difluoro-5,12-bis(triethylsilylethynyl) anthradithiophene produced devices with thin film hole mobilities greater than 1 cm2/Vs. The result suggested that the device is not contact limited rather this high performance OTFTs are due to the contact induced crystallinity of the organic semiconductor.

Our group has previously shown that small changes to molecular structure result in large changes to device properties and stability in organic electronic applications. By functionalizing aromatic heteroacenes with group 14 and group 16 elements, it is possible to control morphology and improve stability for a variety of applications such as thin film transistors and solar cells. Functionalization within the heteroacene core led to changes in electronic structure as observed by electrochemistry and light absorption. By substituting down the periodic table, the carbon heteroatom bond length increased, leading to subtle changes in crystal packing. Absorption maxima were red-­‐shifted and stability to light decreased. Substitution of group 14 elements to the solubilizing ethynyl groups attached to the heteroacene also had an effect on crystallization and stability. Substitution of silicon with carbon decreased solubility as well as stability to light. Substitution with germanium also decreased stability to light, but close contacts within the crystal structure and solubility in nonpolar organic solvents increased.

Soluble organic semiconductors have attracted interest due to their potential in making flexible and cheap electronics. Though their use is being implemented in electronics today, the conduction mechanism is still under investigation. In order to study the charge transport, this study examines the position, voltage, and frequency dependence of charge induced changes in far infrared absorption in soluble organic semiconductors in thin-film transistor structures. Measurements are compared to a simple model of a one-dimensional conductor which gives insight into the charge distribution and timing in devices. Main results of the study are dynamic measurements of charge taken by varying the frequency of the applied gate voltage while observing signal at one position within the transistor; mobility values obtained from a comparison to the one-dimensional model compare well with standard current-voltage measurements. Two small molecule soluble organic semiconductors were studied: 6,13 bis(triisopropylsilylethynyl)-pentacene and fluorinated 5,11 bis(triethylsilylethynyl) anthradithiophene.