Monthly Archives: May 2015

CMOS BEOL-embedded z -axis accelerometer

A first reported complementary metal-oxide semiconductor (CMOS)-integrated acceleration sensor obtained through isotropic inter-metal dielectric (IMD) etching of a back-end-of-line (BEOL) integrated circuit interconnection stack, without any additional substrate etching steps, is presented. The mechanical device composed of a CMOS-process 8 μm-thick metal-via-metal stack of 135 μm diameter and suspended 2.5 μm over a bottom fixed electrode, has a resonance frequency of 20 kHz, a sensing capacitance of 50 fF with sensitivity 14 aF/G and it is integrated on the same substrate with a simple low-noise amplifier reaching 25 mG of RMS noise measured from 0.25 to 100 Hz bandwidth.

Response enhancement mechanism of NO2 gas sensing in ultrathin pentacene field-effect transistors

Publication date: September 2015 Source:Organic Electronics, Volume 24 Author(s): Misbah Mirza , Jiawei Wang , Liang Wang , Jun He , Chao Jiang By optimization of structural and physical–chemical properties at a precision level of molecules, organic sensing devices seek to realize the state of the art in monolayer based device applications. In our work, pentacene ultrathin film transistor has been integrated into the implement of a gas sensor based on an increase in its mobility and a shift of its threshold voltage. A limit of detection of pentacene monolayer field-effect transistor was found to be at sub ppm level when it is applied for detection of NO2. Compared with a thick layer sensor device, the pentacene monolayer NO2 sensor has boosted up sensing response with three orders of magnitude. An enhancement of high selectivity and response mechanism can be understood with a reasonable description emphasizing on the 2D transport characters and a series of gauzy interplay for monolayer pentacene film with NO2 analyte. Graphical abstract

Local-Degradation-Induced Threshold Voltage Shift in Turned-OFF Amorphous InGaZnO Thin Film Transistors Under AC Drain Bias Stress

Local degradation caused by drain bias ( $V_{mathrm {mathbf {DS}}}$ ) stressing is recently considered as a key issue in amorphous InGaZnO (a-IGZO) thin film transistors (TFTs). In this letter, we investigate the instability of turned-OFF a-IGZO TFTs under ac $V_{mathrm {mathbf {DS}}}$ stressing. The negative threshold voltage shift, which was well fitted by a stretched exponential function, was accelerated with increasing duty cycle despite the same effective stress time. A capacitance measurement reveals that a higher duty cycle induced more donor states near the drain, implying that the stretched-exponential time dependence cannot be fully explained by trapping mechanism. Temperature-dependent $tau $ followed the Arrhenius relation, whereas $beta $ showed unusual temperature dependence in contrast to that under dc $V_{mathrm {mathbf {DS}}}$ stressing. These findings suggest an additional origin such as a stress release effect under an ac $V_{mathrm {mathbf {DS}}}$ stress other than hopping/tunneling mechanism.

Low-Voltage a-InGaZnO Thin-Film Transistors With Anodized Thin HfO<sub>2</sub> Gate Dielectric

Low-voltage amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs) with thin HfO2 gate dielectric grown by anodic oxidation (anodization) method are investigated. The morphological and electrical properties of the anodized thin HfO2 film are studied. It is shown that the as-grown HfO2 film with an equivalent oxide thickness of 3.8 nm has a low leakage current density of $3.6 times 10^{-8}$ A/cm $^{2}$ at 1 MV/cm and high dielectric constant of $sim 21.$ The room-temperature fabricated a-IGZO TFTs with the anodized HfO2 gate dielectrics exhibit a low threshold voltage of −0.15 ± 0.08 V, small subthreshold swing value of 109 ± 4 mV/decade, reasonable saturation mobility of 8.1 ± 0.2 cm $^{2}$ /Vs, and an ON/OFF current ratio exceeding $1 times 10^{7}$ .

Domain fracture and recovery process of metal phthalocyanine monolayers via NO2 and H2O

CuPc ultrathin films (5 monolayers) are employed to detect NO2 in chemFETs [organic thin film transistors (OTFTs)]; while the NO2 causes OTFT degradation, H2O restores OTFT performance. To develop an atomic understanding of this H2O induced performance recovery, NO2/CuPc/Au(111) was exposed to H2O, then observed using ultrahigh vacuum scanning tunneling microscopy. After dosing NO2 (10 ppm for 5 min) onto CuPc monolayers under ambient conditions, domain fracture is induced in CuPc monolayers, and CuPc aggregates are formed near new grain boundaries, consistent with dissociative O adsorption between CuPc molecules and Au(111). Conversely, after exposing H2O onto a fractured CuPc monolayer for 30 min, fractured domains merge, then large area domains are generated. As the duration of H2O exposure increases to 4 h, second layer growth of CuPc molecules is observed on the CuPc monolayers consistent with H2O breakdown of CuPc aggregates which have formed at the domain boundaries. The results are consistent with H2O driving the removal of atomic O between CuPc molecules and Au(111) consistent with previous sensing results.

Lithium Ion Assisted Hydration of Metal Ions in Non-Aqueous Sol-Gel Ink for High Performance Metal Oxide Thin-Film Transistors

J. Mater. Chem. C, 2015, Accepted ManuscriptDOI: 10.1039/C5TC00341E, PaperJee-Ho Park, Jin Young Oh, Hong Koo Baik, Tae Il LeeThe role of Li ions in lowering the dehydroxylation temperature of non-aqueous sol-gel inks for the metal oxide thin film transistor (TFT) was demonstrated for the first time. As a...The content of this RSS Feed (c) The Royal Society of Chemistry

Blue enhanced vertically stacked quad junction photodetector with opto window

A vertically stacked quad junction photodetector (PD) with an enhanced spectral responsivity for blue light is presented. This PD is implemented in a 0.35 µm high voltage complementary metal-oxide semiconductor (CMOS) technology. In addition, an optical window, an antireflection coating and a modified p+ doping are used to attain the enhancement for blue light. The proposed PD is compared against other state of the art implementations and characterised for its spectral response.

Characteristics of Al-doped ZnO films annealed at various temperatures for InGaZnO-based thin-film transistors

Publication date: 31 July 2015 Source:Thin Solid Films, Volume 587 Author(s): Jaehyeong Lee , Yong Seob Park Aluminum-doped ZnO (ZnO:Al, AZO) thin-films were deposited using a pulsed DC unbalanced magnetron sputtering system. The deposited AZO films were annealed in N2 ambient at various temperatures using a rapid thermal annealing equipment. The influence of the annealing temperature on the structural, electrical, and optical properties of the AZO films was experimentally investigated and the effect of the conductivity of the AZO source/drain (S/D) electrode on the device performance of an oxide-thin film transistor (TFT) was tested. Increasing the annealing temperature resulted in an improvement of the crystallinity of the films. Increasing grain size was found to lead to an increase in the conductivity of the AZO films. The a-IGZO TFTs fabricated with the annealed AZO S/D electrodes showed good performance. Consequently, the performance of the TFT was influenced by the conductivity of the AZO film, which was related to its structural properties.

The effects of electric field and gate bias pulse on the migration and stability of ionized oxygen vacancies in amorphous In?Ga?Zn?O thin film transistors

Oxygen vacancies have been considered as the origin of threshold voltage instability under negative bias illumination stress in amorphous oxide thin film transistors. Here we report the results of first-principles molecular dynamics simulations for the drift motion of oxygen vacancies. We show that oxygen vacancies, which are initially ionized by trapping photoexcited hole carriers, can easily migrate under an external electric field. Thus, accumulated hole traps near the channel/dielectric interface cause negative shift of the threshold voltage, supporting the oxygen vacancy model. In addition, we find that ionized oxygen vacancies easily recover their neutral defect configurations by capturing electrons when the Fermi level increases. Our results are in good agreement with the experimental observation that applying a positive gate bias pulse of short duration eliminates hole traps and thus leads to the recovery of device stability from persistent photoconductivity.

The effects of electric field and gate bias pulse on the migration and stability of ionized oxygen vacancies in amorphous In–Ga–Zn–O thin film transistors

Oxygen vacancies have been considered as the origin of threshold voltage instability under negative bias illumination stress in amorphous oxide thin film transistors. Here we report the results of first-principles molecular dynamics simulations for the drift motion of oxygen vacancies. We show that oxygen vacancies, which are initially ionized by trapping photoexcited hole carriers, can easily migrate under an external electric field. Thus, accumulated hole traps near the channel/dielectric interface cause negative shift of the threshold voltage, supporting the oxygen vacancy model. In addition, we find that ionized oxygen vacancies easily recover their neutral defect configurations by capturing electrons when the Fermi level increases. Our results are in good agreement with the experimental observation that applying a positive gate bias pulse of short duration eliminates hole traps and thus leads to the recovery of device stability from persistent photoconductivity.