Device layout dependence of PBTI in back-gated IGZO TFTs

The attractive electrical and processing properties of IGZO-based TFTs make these devices promising in various applications, but primarily in BEOL logic and DRAM cells [1,2]. IGZO has been shown to meet the performance requirements of many applications such as display and DRAM selectors [2]. However, the reliability of industry relevant gate-dielectric based IGZO devices has been only recently tackled [3,4]. In addition, the role of device layout and channel geometry (depending on the target application) has not been investigated. In this work we systematically study BTI degradation in 2 main families of back-gated IGZO transistors based on a 10nm thermally grown SiO2 as gate-dielectric, each one differing in S/D access geometry and/or channel width. In the first one, the S/D contacts have very large area with ~5000μm2 (M0 devices), while the second one is based on much smaller contact area of 135nm × device width W (M1 device) (Fig1, left). For each family, gate lengths Lg spanning 2 orders of magnitude (from ~200nm to ~30μm) are investigated to detect short channel effects. Vth0 is extracted at a fixed current level of 100pA×W/L for both architectures (Fig 1., middle). While M0 devices suffer from a decrease of Vth0 as a function of Lg, the Vth of M1 devices is very stable for all measured Lg. Please click Download on the upper right corner to see the full abstract

Spinel, an overlooked crystalline phase of Igzo

In the family of semiconducting oxides, InGaZnO4 (IGZO) is most attractive due to the absence of mobile holes and the preservation of a relative high electron mobility when the material is in the amorphous phase. Especially this last characteristic enables low deposition temperature (Td), beneficial for the application as semiconducting channels of thin film transistors (TFT) in optical displays and 3D memory elements. However, a disadvantage related to the amorphous phase is the distribution of bonding energies of oxygen anions, which is directly related to the distributed distances with respect to the neighboring metal cations [1], leading to free electron formation readily at low temperature. Please click Download on the upper right corner to see the full abstract

Amorphous Metal-Oxide Semiconductor based Thin-Film Electronic Devices for RF Applications on Foil (Dunne-film elektronica voor RF toepassingen op folie gebaseerd op amorfe metaaloxide halfgeleiders)

In recent years, fast progress was made in the technology ofthin-film semiconductor devices based on organic semiconductors (suchaspentacene and derivatives) and oxides, such as Indium-Gallium-Zinc-Oxide(GIZO). In particular this latter semiconductor offers over amorphous siliconthe advantages of a much higher carrier mobility, ofthe order of 10 cm2/Vs,and room temperature processing, making it fully compatible with plasticsubstrates. This new technology opens the way to circuits and systemsfabricated directly on flexible plasticfoil. RFID transponders and tags areone type of application that will greatly benefit from this opportunity. Thegoal of this project is the realization of RF front-endsfor passiveUHF RFID tags on foil. An RF front-end consists of an antenna, arectifier and possibly charge pumps. It captures the electromagnetic field ofan interrogator (also called reader ) and converts it to a DC power supplythat can power, for instance, a transponder chip. Furthermore, it permits toencode data on the RF carrier and transmit that encoded data from thetransponder chip to the interrogator. The crucial element of this circuit isthe diode that must operate at ~1GHz, providing high rectifying rates and lowloses. Among different alternatives, rectifiers based on organic Shottky diodesoperating at HF (13,56MHz) were already developped[1,2], but still nodevice based on organic and/or oxides semiconductors operating at UHF frequencywas shown.In order to accomplish such objective, besides of Shottky diodes,different topologies will be studied, as: pn-junction, tunneling diode,pin-diode, transistor diode, etc. In order to develop oxide based UHF diodes and extract allits potentiality, however, it is crucial to understand the energy levelalignment at the interfaces. Although much work have been done in the lastyears on organic/organic and organic/inorganic interfaces[3,4], not alot was investigated on oxide/organic and oxide/inorganic interfaces, partiallydue to the only recent development of oxide based semiconductors devices[5].Thus, this project will also examine the behavior of oxide/metals andoxide/semiconductors complexes via different techniques such as UPS, XPS, PES andCV measurements. Allied to that, firstprinciple calculations will also be performed to understand the energy levelalignment and band structure of a-GIZO in more detail.1 S.Steudel etal., Nature Materials 4, 597-600(2005).2K. Myny et al., Appl. Phys. Lett.93, 093305 (2008).3 H. Ishii et al., Adv. Mater. 11,605-625 (1999).4 S. Braun et al., Adv. Mater. 21,1450-1472 (2009).5K. Nomura et al., Nature 432, 488-492(2004).status: publishe

Deep-level transient spectroscopy on an amorphous InGaZnO4 Schottky diode

The first direct measurement is reported of the bulk density of deep states in amorphous IGZO (indium-gallium-zinc oxide) semiconductor by means of deep-level transient spectroscopy (DLTS). The device under test is a Schottky diode of amorphous IGZO semiconductor on a palladium (Pd) Schottky-barrier electrode and with a molybdenum (Mo) Ohmic contact at the top. The DLTS technique allows to independently measure the energy and spatial distribution of subgap states in the IGZO thin film. The subgap trap concentration has a double exponential distribution as a function energy, with a value of ∼10 19 cm-3 eV-1 at the conduction band edge and a value of ∼1017 cm-3 eV-1 at an energy of 0.55 eV below the conduction band. Such spectral distribution, however, is not uniform through the semiconductor film. The spatial distribution of subgap states correlates well with the background doping density distribution in the semiconductor, which increases towards the Ohmic Mo contact, suggesting that these two properties share the same physical origin. cop. 2014 AIP Publishing LLC

Deep-level transient spectroscopy on an amorphous InGaZnO4 Schottky diode

The first direct measurement is reported of the bulk density of deep states in amorphous IGZO (indium-gallium-zinc oxide) semiconductor by means of deep-level transient spectroscopy (DLTS). The device under test is a Schottky diode of amorphous IGZO semiconductor on a palladium (Pd) Schottky-barrier electrode and with a molybdenum (Mo) Ohmic contact at the top. The DLTS technique allows to independently measure the energy and spatial distribution of subgap states in the IGZO thin film. The subgap trap concentration has a double exponential distribution as a function energy, with a value of ∼1019 cm−3 eV−1 at the conduction band edge and a value of ∼1017 cm−3 eV−1 at an energy of 0.55 eV below the conduction band. Such spectral distribution, however, is not uniform through the semiconductor film. The spatial distribution of subgap states correlates well with the background doping density distribution in the semiconductor, which increases towards the Ohmic Mo contact, suggesting that these two properties share the same physical origin.status: publishe

Impact of etch stop layer on negative bias illumination stress of amorphous indium gallium zinc oxide transistors

In this work we show that the negative bias illumination stress (NBIS) of amorphous Indium Gallium Zinc Oxide (a-IGZO) transistors with an etch stop layer (ESL) deposited by physical vapor deposition (PVD) is substantially better than the NBIS of devices where the ESL layer is deposited by plasma enhanced chemical vapor deposition (PECVD). Both devices show similar transistor characteristics and bias stress in the dark but under NBIS conditions at 425 nm, PVD ESL based transistors show much less threshold voltage shift. The reduction in deep defects due to passivation by PVD layer is responsible for improved performance under NBIS.status: publishe

Interpretation of frequency dependent capacitance-voltage curves of amorphous Indium Gallium Zinc Oxide (a-IGZO) thin film transistors

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Gigahertz Operation of a-IGZO Schottky Diodes

IGZO film, which we fully measure and characterize, and how that affects the performance and optimization of the diodes. We measure our diodes in rectifiers, which operate up to 1.1 GHz. Finally, we show that these rectifiers can be fully modeled in SPICE using diode parameters extracted from electrical measurements.status: publishe