Organic Dielectric Materials Research Articles

A facile strategy for preparing low dielectric polybutadienes with ultra-low dielectric loss and enhanced thermal stability

With the rapid development of high speed and high frequency communication, organic low dielectric (low-k) materials with both ultra-low dielectric constant (Dk) and ultra-low dielectric loss (Df) are urgently required to ensure signal transmission speed and reliability. 1,2-polybutadiene (1,2-PB) is renowned for its excellent dielectric properties, making it used in high-frequency printed circuit boards (PCBs). However, its poor thermal stability and mechanical properties hinder its application which requires persistent stability. To address this issue, a series of thermal-crosslinkable benzocyclobutene (BCB)-modified PBs were synthesized through a hydrosilylation reaction. These cured PBs exhibited significantly enhanced thermal stability with the glass transition temperature (Tg) exceeding 400 °C. In particular, they displayed ultra-low Dk (2.32–2.41) and ultra-low Df (<0.001). It was found that the properties of cured PBs were related to BCB loadings. Among the cured polymers, PB-g-B30 demonstrated the optimal dielectric properties with a Dk of 2.34 and a Df of 3.6 × 10−4. Subsequently, a PB-g-B30/glass fiber laminate was fabricated, exhibiting superior dielectric and comprehensive properties when compared to commercial low-k laminates. This study provides a facile method to develop PBs with ultra-low Dk and Df and enhanced thermal stability. The outstanding comprehensive properties indicate their potential as low-k materials in high-frequency communication applications.

Electrostatic Correlations Lead to High Capacitance in Zwitterion-Containing Thin Films.

A novel zwitterion composed of an imidazolium tethered to an anionic sulfonyl(trifluoromethane sulfonyl)imide group was prepared as an alternative dielectric material to traditional ionic liquids. The zwitterion not only melted below 100 °C but also proved to be nonhygroscopic. High-capacitance organic dielectric materials were obtained by blending this compound with poly(methyl methacrylate) over a range of concentrations and thicknesses. Above a specific temperature and concentration, films exhibit a capacitance nearly equivalent to that of an electrostatic double layer, approximately 10 μF/cm2, regardless of their thickness. Grazing-incidence wide-angle X-ray scattering experiments suggest that the zwitterions adopt a lamellar ordering at their surface above a critical concentration. The observed ordering is correlated with a 1000-fold increase in capacitance. The behavior suggests that the zwitterions exhibit strong electrostatic correlations throughout the film bulk, pointing the way toward a novel class of organic dielectric materials.

Versatile Landscape of Low-k Polyimide: Theories, Synthesis, Synergistic Properties, and Industrial Integration.

The development of microelectronics and large-scale intelligence nowadays promotes the integration, miniaturization, and multifunctionality of electronic and devices but also leads to the increment of signal transmission delays, crosstalk, and energy consumption. The exploitation of materials with low permittivity (low-k) is crucial for realizing innovations in microelectronics. However, due to the high permittivity of conventional interlayer dielectric material (k ∼ 4.0), it is difficult to meet the demands of current microelectronic technology development (k < 3.0). Organic dielectric materials have attracted much attention because of their relatively low permittivity owing to their low material density and low single bond polarization. Polyimide (PI) exhibits better application potential based on its well permittivity tunability (k = 1.1-3.2), high thermal stability (>500 °C), and mechanical property (modulus of elasticity up to 3.0-4.0 GPa). In this review, based on the synergistic relationship of dielectric parameters of materials, the development of nearly 20 years on low-k PI is thoroughly summarized. Moreover, process strategies for modifying low-k PI at the molecular level, multiphase recombination, and interface engineering are discussed exhaustively. The industrial application, technological challenges, and future development of low-k PI are also analyzed, which will provide meaningful guidance for the design and practical application of multifunctional low-k materials.

Next Level of 1/1 μm Line and Space Copper Redistribution Layer Fabrication with Organic Dielectric Materials

An electrical reliability of fine copper redistribution layer (RDL) with 1/1 μm line and space fabricated by using positive photosensitive polyimide (PSPI) has been demonstrated. The polyimide containing flexible molecular units in PSPI was introduced, in assumption to increase the entanglement of each polymer chain with a design concept of polymer backbone to enhance mechanical and thermal reliability. To conduct a series of tests, test vehicles with semi-additive copper RDL with 1/1 μm line and space were fabricated with Toray’s PSPI for electrical reliability test. Through a series of electrical reliability tests utilizing our test vehicles, PSPI out-performed the phenol-based resin, which has been proven to have excellent mechanical and thermal stabilities when compared with other resins. 1/1 μm line and space electrodes after electrical reliability tests were also observed and cross-sectioned. The observation of electrodes clearly showed oxidation-reduction of the electrodes on anode and cathode, respectively. On the cathode, copper particles of several nm in diameter were formed on the PI film surrounding the copper wiring. On the anode, copper oxide layers of about 100 nm thickness were observed on the copper wiring surface, which turned out to be Cu2O when analyzed with Electron Energy-Loss Spectroscopy (EELS) measurement.

Intrinsically flexible displays: key materials and devices.

Continuous progress in flexible electronics is bringing more convenience and comfort to human lives. In this field, interconnection and novel display applications are acknowledged as important future directions. However, it is a huge scientific and technical challenge to develop intrinsically flexible displays due to the limited size and shape of the display panel. To address this conundrum, it is crucial to develop intrinsically flexible electrode materials, semiconductor materials and dielectric materials, as well as the relevant flexible transistor drivers and display panels. In this review, we focus on the recent progress in this field from seven aspects: background and concept, intrinsically flexible electrode materials, intrinsically flexible organic semiconductors and dielectric materials for organic thin film transistors (OTFTs), intrinsically flexible organic emissive semiconductors for electroluminescent devices, and OTFT-driven electroluminescent devices for intrinsically flexible displays. Finally, some suggestions and prospects for the future development of intrinsically flexible displays are proposed.

Eliminating Leakage Current in Thin‐Film Transistor of Solution‐Processed Organic Material Stack for Large‐Scale Low‐Power Integration

AbstractFor organic thin‐film transistors (OTFTs) made of solution processed stacks of organic semiconductor and dielectric materials, it is a grand challenge to eliminate the leakage current paths. With a top‐gate bottom‐contact structure, this work introduces a strong dipole interfacial layer made of self‐assembled monolayer (SAM) molecules at metal‐semiconductor contacts to suppress minority carrier injection for low leakage and stable operation, while not affecting majority carrier injection. Both gate insulator (GI) leakage and parasitic leakage in the device architecture are also effectively suppressed with a sputtering‐resistant polymer GI layer and photolith patterned OSC islands, respectively. The devices present a decent mobility with a typical value of 1.98 cm2 V–1 s–1, record‐low leakage current at 10–18 A µm−1 and large ON/OFF ratio (&gt;1010) in a wide gate voltage range (100 V), reaching the theoretical limit and also the best level of inorganic counterparts despite much lower processing temperature (120 °C). Manufacturability of the material stack is verified on a 200 mm × 200 mm substrate and the fabricated 4.7 in. active‐matrix organic light‐emitting diode display, integrating more than 150 000 OTFTs, can be operated at ultra‐low frame‐rate (0.1 Hz) for power saving.

High energy storage density and low energy loss achieved by inserting charge traps in all organic dielectric materials

An innovative strategy of introducing space charge traps to dielectric materials is developed by copolymerization of MMA with conjugated VK, which enables superior energy storage performance (Ue = 15.7 J cm−3 @ 750 MV m−1, η = 88%).

Reversible structural phase transition and dielectric behaviour associated with the ordering-disordering of molecular rotation in an organic supramolecular solid

• A pure organic single crystal, [H 2 dabco][Ma] 2 (1) undergoes a reversible structural phase transition at ~250 K and possesses a unique three-dimensional network structure. • The origin of the phase transition and the dielectric anomaly is ascribed to the order-disorder transformation of [H 2 dabco] 2+ cations and the resulting relative molecular rotation from the equilibrium position. A pure organic single crystal, [H 2 dabco][Ma] 2 ( 1 ) ([H 2 dabco] 2+ = diprotonated 1,4-diazabicyclo[2,2,2]octane, [Ma] = malic acid), was prepared and characterised. Differential scanning calorimetry, potential energy calculations, and dielectric property measurements indicated the occurrence of a reversible structural phase transition at ~250 K, while single-crystal X-ray diffraction revealed that 1 possesses a unique three-dimensional network structure with the [H 2 dabco] 2+ cation bridged by two [Ma] − anions through N–H•••O hydrogen bonds. At 296 K, the [H 2 dabco] 2+ cation exists in a rotationally disordered state and is fixed into the two-dimensional layered structure of [Ma] − anions through N–H•••O hydrogen bonds. Upon cooling to 100 K, the above cation is frozen into an ordered state and shifts towards the top anion and the bottom anion at one end along the hydrogen bond. The origin of the phase transition and the dielectric anomaly is ascribed to the order-disorder transformation of [H 2 dabco] 2+ cations and the resulting relative molecular rotation from the equilibrium position. One pure organic single crystal, [H 2 dabco][Ma] 2 ( 1 ) ([H 2 dabco] 2+ = diprotonated 1,4-diazabicyclo[2,2,2]octane, [Ma] ‐ = malic acid), was synthesized and underwent the structural phase transitions from space group P 2 1 /c to C 2/c. The conformations of dabco rings in the RTP (296 K) and the LTP (100 K) are markedly different owing to the order-disorder rotation of [H 2 dabco] 2+ cations. This results in the phase transition and dielectric anomaly of compound and provides useful strategies of finding new organic dielectric materials.

Optimizing the Interdomain Spacing in Alicyclic Polythiourea toward High-Energy-Storable Dielectric Material.

Organic dielectric materials have been widely developed and investigated for energy storage capacitors. However, challenges remain in terms of the relatively low dielectric constant and energy density. Enhancing the dipolar polarization to increase the dielectric constant is considered to be an effective way to improve the energy density of polymer dielectrics. Herein, enlightened by the chain-packing structure that affects the dipolar relaxation behavior, a simple and low-cost approach is proposed to tailor the interdomain spacing in an alicyclic polythiourea (PTU) by changing quenching temperatures and further facilitate the dipolar polarization. It is found that the large interdomain spacing is beneficial to promote the localized motion of segmental chains in amorphous regions, but at the same time inevitably reduces the dipole density. Therefore, in order to achieve the highest dielectric constant in the PTU, there is an optimal value for the interdomain spacing. It is worth noting that the dielectric constant of PTU increases from 5.7 to 10, and thus the energy density increases by 53% to 16.3 J cm-3 . It proposes a simple and feasible strategy to further improve the energy density through optimizing the interdomain spacing toward high-energy-storable dielectric material.

Effect of hydroxyl group in polymeric dielectric layer on the performance of organic thin-film transistors and their application for NO2 gas sensor

Poly(vinyl alcohol) (PVA) as a conventional polymer dielectric material which possesses excellent insulating performance by cross-linking of the hydroxyl-rich group (–OH) has been utilized extensively in organic thin-film transistors (OTFTs). In this work, a novel strategy for OTFTs, constructing with tandem dielectric films, is studied. The air stability of OTFTs can be conveniently modulated by the construction of tandem dielectrics. Herein, with the optimization for the dielectric structures and interface engineering, a holistic understanding of the hydroxyl group for the performance of OTFTs and OTFT-based gas sensors is provided. Implementing the interface properties affords double dielectric OTFTs that deliver a remarkable responsivity for 10 ppm NO2 nearly 62% and triple dielectric OTFTs that maintain a slight fluctuation in their electrical performance during 10-day atmospheric storage, respectively. The enhancement of air stability of OTFTs and sensing performance for NO2 can be attributed to the passivation controlling effect of PVA, and these results demonstrate that the simple and effective method provides new insight into the design of functional groups of organic dielectric materials for high-performance, air-stable OTFTs and high responsivity for OTFT-based gas sensors.

Process and characterization of photo-definable organic–inorganic dielectric for wafer level packaging

The introduction of an organic–inorganic dielectric material into the redistribution layers in fan-out wafer level packaging technology has been investigated to improve mechanical stress, thermal stability, and electrical breakdown compared to organic dielectric materials. A photo-definable organic–inorganic dielectric material called polysilsesquioxane (PSSQ) has been studied in this work. The photo-definable PSSQ dielectric allows a simultaneous UV patterning and curing process. A PSSQ sample was prepared by spin-coating on a 6-in. Si wafer, pre-baking at 100 °C for 5 min, UV exposure, and then PGMA developing. The cured PSSQ films have a dielectric constant from 2.0 to 2.38 and dielectric loss from 0.0001 to 0.005. In addition, the 2 μm line patterns were obtained after 10 min of UV exposure. It has been demonstrated that PSSQ dielectric materials can provide excellent process capability of simultaneous UV patterning and curing process.

Development of High-k Polymer Materials for Use as a Dielectric Layer in the Organic Thin-Film Transistors

In this article, we developed a series of novel high dielectric polymers based on 5-TPM-co-HEMA-co-GMA (TP) and 5-CTPM-co-HEMA-co-GMA (TP–CN) containing alkylated terphenyl and alkylated terphenyl with a cyano group, respectively. These organic insulating materials provide smooth surface topographies, lower leakage current densities (<6 × 10–7 A/cm2 at 2 MV/m), and small dielectric loss (<0.02, 103 to 105 Hz), which display excellent insulating properties. Simultaneously, two kinds of polymer films have higher dielectric constants of 6.8 and 8.6 than other dielectric constants reported in some literatures and most commercial organic dielectric materials. To investigate the potential of TP and TP–CN as gate dielectrics, we successfully prepared bottom-gate top-contact organic thin-film transistors, with para-hexaphenyl (p-6P) as the buffer layer and vanadyl phthalocyanine (VOPc) as the active layer, which yields a higher charge carrier mobility of 0.52 cm2 V–1 s–1 and on/off ratio > 104.

Graphene-based field effect transistor with ion-gel film gate

Graphene is a kind of two-dimensional material with high light transmittance, high mechanical properties and high carrier mobility. The energy band of graphene can be turned by doping and electric field. Researches on the application of graphene to electronic devices focused on field effect transistors. For improving the performance, one generally improves the fabrication process and device structure, but many researchers chose to change the material or structure of dielectric layer. Ion-gel is a kind of mixture of organic polymer mesh structure with good thermal stability and high dielectric value, prepared by macromolecule organic polymer and ionic salt electrolyte material. With the effect of electric field, cations and anions in ion-gel diffuse to form a double charge layer distribution with a charge layer on the surface of material. This capacitance characteristic is similar to that of traditional capacitor. In this paper, ion-gel (PVDF-[EMIM]TF2N) film is used as a dielectric layer material to prepare the bottom-gate graphene-based field effect transistor (GFET), which is compared with the GFET with SiO&lt;sub&gt;2&lt;/sub&gt; bottom-gate, according to electrical characteristic curves. The effect of the ion-gel film on the transconductance, switching ratio and Dirac voltage of the GFET are analyzed. The effect of the vacuum environment and temperature on the GFET performance with ion-gel film gate are also investigated. The results show that in the room-temperature environment, the switching ratio and transconductance of the ion-gel film gate GFET device increase to 6.95 and 3.68 × 10&lt;sup&gt;–2&lt;/sup&gt; mS, respectively, compared with those of the SiO&lt;sub&gt;2&lt;/sub&gt; gate GFET, while the Dirac voltage decreases to 1.3 V. The increase in transconductance and switching ratio of ion-gel film gate GFETs are mainly due to the high capacitance of ion-gel film compared with those of conventional SiO&lt;sub&gt;2&lt;/sub&gt; gate dielectrics. There will be more carriers inside the graphene while in the carrier accumulation region of GFET transfer characteristic curve, which makes graphene more conductive. The Dirac voltage of ion-gel film gate GFET can be reduced to 0.4 V in the vacuum environment; as the temperature increases, the transconductance of GFET can increase up to 6.11×10&lt;sup&gt;–2&lt;/sup&gt; mS. The results indicate that the ion-gel film-based graphene field effect transistor shows good electrical properties in serving as high dielectric constant organic dielectric materials.

Измерение степени полимеризации полимерных материалов изоляционной системы высоковольтного оборудования

The use of polymeric materials polymerization degree (PD) as a parameter from which the state of power equipment insulation system as a whole is estimated imparts much importance and significance to the PD measurement problem. The possibility of using the PD value as a parameter for estimating the state of power equipment items that have been in operation for a long time also attracts the attention of specialists. In this regard, practical methods for measuring the spectrum of dielectric absorption currents, which make it possible to monitor the polymeric material polarization degree, are of special interest. These methods are based on the theoretical concepts about the motion of a charged particle as a Stokes body in dielectric medium with specific viscosity ƞsp under the effect of a constantly applied electric field. To this end, the conductivity of a specially formed two-layer dielectric medium is monitored in the method being analyzed. One of these layers is a sample of the material being monitored, and the second one, which is in close contact with the first one, is a material the viscosity of which is known or can be easily measured using accessible methods, as in the case of a liquid dielectric. The proposed method for determining the PD of organic dielectric materials by measuring the spectrum of dielectric absorption currents is essentially a dielectric medium viscosity monitoring technique. It is exactly this parameter that governs the charged particle motion pattern in a dielectric and, hence, the characteristic features of the spectrum of dielectric absorption currents in the insulation gap being monitored. Owing to the clear physical principles laid down in the proposed method for estimating the polymerization degree, commercial availability of the equipment for its implementation, the availability of user-friendly software, and the simplicity of interpretation and analysis of the obtained results, the new method significantly extends the existing tools for assessing the insulation system state and determining the remained lifetime of operating power equipment.

Subthreshold-Operated Low-Voltage Organic Field-Effect Transistor for Ion-Sensing System of High Transduction Sensitivity

A combination of the ion-sensitive organic field-effect transistor (ISOFET) transducer with silicon chips can utilize the strengths of both technologies for developing ubiquitous sensor systems. For optimal design of such a system, the transduction sensitivity of the ISOFET needs to be maximized. In this article, OFETs of different subthreshold swing (SS) values are fabricated using a solution processed organic semiconductor and dielectric materials to experimentally prove the dependence of the transduction sensitivity on the SS. Further ion-sensing measurement results show that the OFET of small SS (80mVdec) realized by both large gate dielectric capacitance and significantly reduced subgate density of states at the channel can help to achieve similar sensitivity with that of the silicon FET but with two-order lower power consumption.

Deposition method and performance of SiO2 as a dielectric material for beam steering electrowetting devices

Electrowetting has the potential to be applied to steering and concentrating sunlight using liquid lenses. However, the performance of electrowetting devices depends on the careful selection/fabrication of their constituent dielectric material. The dielectric material should have high optical transparency, chemical stability, high relative permittivity, be relatively thin and have a high breakdown voltage. Recent studies noted that inorganic dielectric materials such as SiO2 are more suitable for beam steering compared to organic dielectric materials such as fluoropolymers or parylene C for example. When optical transmission is not required, electrowetting devices are fabricated by thermally growing SiO2 on top of silicon wafers. However, this deposition method is not suitable for beam steering electrowetting devices as the silicon substrate is not optically transparent. In this paper, we investigated the performance of SiO2 as a dielectric material for beam steering electrowetting devices. Specifically, we measured the contact angle modulation capability of SiO2 produced by electron-beam and sputtering deposition methods and correlated the results with morphological defects of the SiO2 layer introduced by the deposition methods. We investigated the effect of annealing and the performance with ionic and DI water. Finally, we compared the performance of SiO2 with other dielectric materials such as PDMS and Ta2O5 in air/water and silicone oil/water medium.

(Invited) Design of Bowl-Shaped Molecules Toward Dielectric Responsive Materials

Organic dielectric materials that can respond to electric fields have drawn much attention because of their potential applications to memory and sensing devices. One of the essential requirements for organic dielectric materials is the ability of changing the overall dipole moment in response to external electric fields. In this context, sumanene derivatives featuring a bowl-shaped skeleton are attractive, because they undergo a bowl-to-bowl inversion, which is accompanied by the inversion of the molecular dipole. As the bowl-to-bowl inversion would be facilitated in soft mesophases, liquid-crystalline (LC) sumanenes, for example, are expected to provide an interesting building block for the design of organic dielectric materials. While many examples of crystalline sumanenes have so far been reported, there is no sumanene derivative that can exhibit an LC mesophase. We recently found that sumanene, when carrying six alkyl side chains, successfully shows an LC mesophase over a wide temperature range. Herein, we report the synthesis, assembly structure, and dielectric properties of the new hexa-substituted sumanenes. Figure 1

Low Hysteresis Carbon Nanotube Transistors Constructed via a General Dry-Laminating Encapsulation Method on Diverse Surfaces.

Electrical hysteresis in carbon nanotube thin-film transistor (CNTTFT) due to surface adsorption of H2O/O2 is a severe obstacle for practical applications. The conventional encapsulation methods based on vacuum-deposited inorganic materials or wet-coated organic materials have some limitations. In this work, we develop a general and highly efficient dry-laminating encapsulation method to reduce the hysteresis of CNTTFTs, which may simultaneously realize the construction and encapsulation of CNTTFT. Furthermore, by virtue of dry procedure and wide compatibility of PMMA, this method is suitable for the construction of CNTTFT on diverse surface including both inorganic and organic dielectric materials. Significantly, the dry-encapsulated CNTTFT exhibits very low or even negligible hysteresis with good repeatability and air stability, which is greatly superior to the nonencapsulated and wet-encapsulated CNTTFT with spin-coated PMMA. The dry-laminating encapsulation strategy, a kind of technological innovation, resolves a significant problem of CNTTFT and therefore will be promising in facile transferring and packaging the CNT films for high-performance optoelectronic devices.

Inorganic–organic hybrid switchable dielectric materials with the coexistence of magnetic anomalies induced by reversible high-temperature phase transition

We reported an inorganic–organic switchable dielectric hybrid, which shows the coexistence of magnetic responses as another potential physical channel to structural phase transition.

Organic Single Crystals: An Essential Step to New Physics and Higher Performances of Optoelectronic Devices

Organic Single Crystals: An Essential Step to New Physics and Higher Performances of Optoelectronic Devices