In this presentation, I will discuss advancements in monolayer organic transistors using C10-DNTT. We can directly achieve large, crystallized C10-DNTT areas on silicon substrates, but compatibility with traditional methods is limited. I'll explain the principles of electrode transfer and semiconductor patterning stamps for fabricating OFETs with 2µm channel lengths without chemicals or damage. We integrated the monolayer OFET into an AC/DC rectifying circuit, achieving a 17.3 MHz cutoff frequency.
In this talk, I will focus on the meniscus guided coating (MGC) method for the OFET fabrications. We will demonstrate and elucidate why the organic monolayer OFETs developed by MGC would show outstanding contact resistance values under staggered structure especially during low source-drain bias (VDS) operations. The device under study is 2,9-didecyldinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C10-DNTT) monolayer with the van der Waals integration of metal electrodes. I will deviate the access resistance component and interface resistance component of the contact resistance. We noticed access resistance of organic semiconductor is extracted under -1 mV drain-source bias, while the Schottky diode at the metal-organic interface is negligible. On the other hand, the diode effect at the metal-organic interface can be amplified by increasing the VDS level and eventually dominates the device performance.
Achieving gigahertz transit frequencies in low-voltage organic thin-film transistors (TFTs) will require a contact resistance below about 1 Ohm-cm [1,2]. A general approach to reduce the contact resistance in organic devices is to modify the surface of the metal contacts with a chemisorbed interface layer, ostensibly by reducing the nominal injection barrier. Combined with a thin gate dielectric, this approach can enable contact resistances below 30 Ohm-cm and transit frequencies above 10 MHz at low voltages in coplanar organic TFTs [3,4]. However, further reduction of the contact resistance depends strongly on non-idealities of the interface other than the nominal barrier height according to the Schottky-Mott limit. We show a detailed study on the efficacy of interface layers based on various thiols to improve the contact resistance in coplanar dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) TFTs. We compare the contact resistance of multiple sets of TFTs to results from ultraviolet photoelectron spectroscopy measurements and find strong evidence that Fermi-level pinning prevents a significant reduction of the contact resistance below about 100 Ohm-cm in DNTT TFTs. Therefore, we conclude that this approach may not be a generally sufficient method by itself to eliminate the contact resistance in organic TFTs.
Organic field effect transistors (OFETs) are the key players of the next generation flexible electronics. In this talk, I will focus on the meniscus guided coating (MGC) method for the OFET fabrications. If one can control the coating parameters well, the MGC method can ensure excellent crystallinity in the small molecules OFETS. This method is also highly compatible with large area deposition for mass production. Four elementary processing parameters (i) shearing speed (v), (ii) solute concentration, (iii) deposition temperature (T) and, (iv) solvent boiling point (Tb) are utilized to analyze crystal growth behavior in the meniscus-guided coating. I will also provide a generalized formula to estimate the effects of these fabrication parameters which can serve as the crystal growth guidelines for the MGC approach. I will also discuss how to use the ultra-low speed version of MGC to develop 2D monolayer organic crystal and long range in-plane ordering.
Flexible transistor active matrix array is fabricated on PEN substrate using all screen-printed gate, source and drain electrodes. Parylene-C and DNTT act as gate dielectric layer and semiconductor, respectively. The transistor possesses high mobility (0.33 cm2V-1 s-1), large on/off ratio (< 106) and low leakage current (~10 pA). Active matrix array consists of 10×10 transistors were demonstrated. Transistors exhibited average mobility of 0.29 cm2V-1s-1 and on/off ratio larger than 104 in array form. In the transistor array, we achieve 75μm channel length and a size of 2 mm × 2 mm for each element in the array which indicates the current screen-printing method has large potential in large-area circuits and display applications.
We have fabricated the transistor memory devices based on SiO2 and polystyrene (PS) hybrid dielectric. The trap states densities with different semiconductors have been investigated and a maximum 160V memory window between programming and erasing is realized. For DNTT based transistor, the trapped electron density is limited by the number of mobile electrons in semiconductor. The charge transport mechanism is verified by light induced Vth shift effect. Furthermore, in order to meet the low operating power requirement of portable electronic devices, we fabricated the organic memory transistor based on AlOx/self-assembly monolayer (SAM)/PS hybrid dielectric, the effective capacitance of hybrid dielectric is 210 nF cm-2 and the transistor can reach saturation state at -3V gate bias. The memory window in transfer I-V curve is around 1V under +/-5V programming and erasing bias.
In semiconductor lasers, key parameters such as threshold current, efficiency, wavelength, and lifetime are closely related to temperature. These dependencies are especially important for high-power lasers, in which device heating is the main cause of decreased performance and failure. Heat sources such as non-radiative recombination in the active region typically cause the temperature to be highly peaked within the device, potentially leading to large refractive index variation with bias. Here we apply high-resolution charge-coupled device (CCD) thermoreflectance to generate two dimensional (2D) maps of the facet temperatures of a high power laser with 500 nm spatial resolution. The device under test is a slab-coupled optical waveguide laser (SCOWL) which has a large single mode and high power output. These characteristics favor direct butt-coupling the light generated from the laser diode into a single mode optical fiber. From the high spatial resolution temperature map, we can calculate the non-radiative recombination power and the optical mode size by thermal circuit and finite-element model (FEM) respectively. Due to the thermal lensing effect at high bias, the size of the optical mode will decrease and hence the coupling efficiency between the laser diode and the single mode fiber increases. At I=10Ith, we found that the optical mode size has 20% decrease and the coupling efficiency has 10% increase when comparing to I=2Ith. This suggests SCOWL is very suitable fr optical communication system.
We have investigated the molecular beam epitaxial growth and characteristics of self-organized InGaAs quantum dot lasers grown directly on silicon utilizing thin (≤2 μm) GaAs buffer layers and quantum dot layers as dislocation filters. Both the photoluminescence intensity and linewidth from quantum dots grown on silicon are comparable to those from similar dots grown on GaAs substrates. Cross-sectional transmission electron microscopy studies indicate that defect-free quantum dots and low defect density quantum dot active regions can be achieved. The best devices are characterized by relatively low threshold current (Jth ~ 900 A/cm2), high output power (> 150 mW), large characteristic temperature (T0 = 244 K) and constant output slope efficiency (≥ 0.3 W/A) in the temperature range of 5 to 95 °C.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.