Chia-Liang Tsai

Nonvolatile transistor memory devices using high dielectric constant polyimide electrets

We report on the nonvolatile memory characteristics of pentacene-based organic field-effect transistors (OFETs) using polyimides, PI(6FDA-TPA-CN), PI(DSDA-TPA-CN), and PI(BTDA-TPA-CN), consisting of electron-donating 4,4′-diamino-4′′-cyanotriphenylamine (TPA-CN) and different electron-accepting dianhydrides as polymer electrets. The dielectric constants of PI(BTDA-TPA-CN), PI(DSDA-TPA-CN), and PI(6FDA-TPA-CN) are 3.44, 3.52, and 3.70, respectively, higher than those (∼3) of common polyimides. Among the polymer electrets, the OFET memory device based on PI(6FDA-TPA-CN) exhibits the highest OFET mobility of 0.5 cm2 V−1 s−1 due to the formation of a pentacene film of large grain size by the hydrophobic surface. The OFET memory devices with the configuration of n+Si/SiO2/PI/pentacene/Au show excellent nonvolatile memory behaviors for bistable switching. The stability for ON and OFF states can be maintained for 104 s with a Ion/Ioff current ratio of 104 for PI(6FDA-TPA-CN). Moreover, the higher dipole moment and larger torsion angle result in the more stable charge transfer complex, accompanied by the largest memory window of 84 V for the fabricated device. The write–read–erase–read (WRER) cycles can be operated over 100 cycles. The present study suggests that the high dielectric constant polyimide electrets with the enhanced capabilities for storing the charges have great potential applications for advanced OFET memory devices.

Flexible, optically transparent, high refractive, and thermally stable polyimide–TiO2 hybrids for anti-reflection coating

In this study, flexible and transparent polyimide–nanocrystalline-titania hybrid optical films with a high titania content (up to 50 wt%) and thickness (15 μm) were prepared from new soluble poly(o-hydroxy-imide)s and fabricated for a three-layer antireflection coating. The hydroxyl groups on the backbone of the polyimides could provide a reaction site for organic–inorganic bonding and resulted in homogeneous hybrid solutions by controlling the mole ratio of titanium butoxide/hydroxyl groups. The well-dispersed nanocrystalline-titania was demonstrated by XRD and TEM measurements. The flexible hybrid films with good surface planarity, thermal dimensional stability, tunable refractive index (1.63–1.80 at 633 nm), and high optical transparency were successfully obtained and further utilized to prepare a three-layer anti-reflection coating, indicating its potential optical applications.

A novel porphyrin-containing polyimide for memory devices

We design a novel solution-processable polyimide ZnPor-t-DSDA with porphyrin moiety (electron donor) and sulfone-containing phthalimide (electron acceptor) for polymer memory applications. The resulting memory device can be switched from low-conductivity (OFF) to high-conductivity (ON) by both positive and negative sweeps, exhibiting symmetry biswitching characteristic with a short retention time (30 s). On the basis of the simulation calculation, the coplanar structure between donor and acceptor units results in charge transferring easily back to its original state after being excited by an electric field.

Novel solution-processable fluorene-based polyimide/TiO2 hybrids with tunable memory properties

A new hydroxyl-containing fluorene-based polyimide FOH-6FPI hybrid with different TiO2 contents was prepared and used for memory device applications. The resulting films exhibited tunable memory properties from DRAM, SRAM, to WROM at different TiO2 concentrations from 0 wt% to 50 wt% with a high ON/OFF current ratio (108).

Electrically programmable digital memory behaviors based on novel functional aromatic polyimide/TiO2 hybrids with a high ON/OFF ratio

A novel solution-processable sulfur-containing poly(o-hydroxy-imide) 3SOH-6FPI with pendant hydroxyl groups and the corresponding polyimide 3SOH-6FPI/TiO2 hybrids were synthesized from diamine 4,4′-bis(4-amino-3-hydroxyphenylthio)diphenylsulfide (3SOH-DA) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and used for memory applications. To enhance the memory behavior, different amounts of TiO2 were introduced into 3SOH-6FPI and the corresponding tunable memory properties were investigated. The hydroxyl groups on the backbone of 3SOH-6FPI could provide reaction sites for organic–inorganic bonding and the homogeneous hybrid thin films could therefore be obtained by controlling the mole ratio of titanium butoxide/hydroxyl groups via sol–gel reaction. The resulting hybrid films having different TiO2 concentrations from 0 wt% to 50 wt% exhibited electrically programmable digital memory properties from DRAM, SRAM, to WORM with a high ON/OFF current ratio (108). Furthermore, from the results of the current–voltage I–V characteristics, the crystalline phase of titania reveals higher trapping ability to increase the retention time in the ON state. In order to get more insight into the switching mechanism of 3SOH-6FPI/TiO2 hybrid memory devices, molecular simulation and electrode effects were also discussed in this study.

Novel solution-processable optically isotropic colorless polyimidothioethers–TiO2 hybrids with tunable refractive index

In this study, a new facile synthetic route was developed to prepare polyimidothioethers–nanocrystalline-titania (PITEs–TiO2) hybrid optical films with a high titania content (up to 50 wt%) and thickness (15 ± 3 μm) from soluble PITEs containing hydroxyl groups. A series of organosoluble PITEs were prepared from the hydroxy-substituted dithiols and various commercial bismaleimides via Michael polyaddition. The hydroxyl groups at the backbone of the PITEs could provide the organic–inorganic bonding sites and resulted in homogeneous hybrid solutions by controlling the mole ratio of titanium butoxide/hydroxyl group. AFM, TEM, and XRD results indicated the formation of well-dispersed nanocrystalline-titania. The flexible hybrid films were successfully obtained and revealed good surface planarity, thermal dimensional stability, tunable refractive index (1.69 to 1.80 at 633 nm), and high optical transparency. A three-layer antireflection coating based on the hybrid films was prepared and showed a reflectance of less than 0.5% in the visible range, indicating its potential optical applications.

Linkage and donor–acceptor effects on resistive switching memory devices of 4-(N-carbazolyl)triphenylamine-based polymers

In order to gain deeper insight into the linkage effect and donor–acceptor effect on memory behavior (from DRAM to WORM), 4-(N-carbazolyl)triphenylamine-based polyimides and polyamides t-butyl-6FPI, t-butyl-DSPI, OMe-6FPI, OMe-DSPI, t-butyl-6FPA, t-butyl-DSPA, OMe-6FPA, and OMe-DSPA were synthesized and their memory behaviours were investigated.

Nonvolatile transistor memory devices based on high-k electrets of polyimide/TiO2 hybrids

Novel nonvolatile memory behaviors of n-type N,N′-bis(2-phenylethyl)-perylene-3,4,9,10-tetracarboxylic diimide (BPE-PTCDI) based organic field-effect transistors (OFET) using the new polyimides (PIs), (poly[9,9-bis(4-(4-amino-3-hydroxyphenoxy)phenyl)fluorene-oxydiphthalimide]) PI(F-ODPA) and (poly[4,4′-bis(4-amino-3-hydroxyphenylthio)diphenyl sulfide-oxydiphthalimide]) PI(3S-ODPA), and their PI/TiO2 hybrids as electrets are reported. The OFET memory devices derived from PI(F-ODPA) with π-conjugated fluorene moieties exhibited a larger memory window (8.6 V), and could be further enhanced by introducing TiO2 (up to 20 wt%) into the PIs. In addition, PI/TiO2 hybrids as electrets for memory devices also could effectively reduce the operating voltage, indicating that the charge transfer capability of TiO2 plays an important role in transferring and storing the charge for OFET memory devices.

Electrochromism and Nonvolatile Memory Device Derived from Triphenylamine-Based Polyimides with Pendant Viologen Units

Three novel solution-processable polyimides containing triphenylamine and pendant viologen moieties are prepared from the newly synthesized diamine and three commercially available dianhydrides. The thermally stable polyimide with strong donor-acceptor charge-transfer possesses write-once read-many-times memory behavior with excellent operation stability. The obtained multicolored electrochromic polymer films reveal ambipolar electrochemical behavior with high optical transmittance contrast of coloration changed from transmissive neutral state to the cyan/magenta/yellow redox states, implying great potential for application in smart window and displays.

Zinc and linkage effects of novel porphyrin-containing polyimides on resistor memory behaviors

A new class of porphyrin-containing polyimides, ZnPor-s-DSDA, ZnPor-t-DSDA, Por-s-DSDA and Por-t-DSDA, were synthesized from porphyrin-containing diamines and 3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride for resistor-type memory applications. The effect of the linkage and zinc metal was investigated by electrochemistry, molecular simulations, and memory behaviors. The memory devices with different retention times derived from polymers ZnPor-s-DSDA (WORM, >3 h) and ZnPor-t-DSDA (DRAM, 30 s) demonstrated the importance of the linkage effect, and the insulation property of polyimides Por-s-DSDA and Por-t-DSDA also implies a crucial memory behavior by metal chelation.