Fraunhofer-Institut für Photonische Mikrosysteme IPMS

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  • Publication
    A Fully Integrated Ferroelectric Thin-Film-Transistor - Influence of Device Scaling on Threshold Voltage Compensation in Displays
    ( 2021)
    Lehninger, D.
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    Ellinger, M.
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    Ali, T.
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    Li, S.
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    Mertens, K.
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    Lederer, M.
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    Olivio, R.
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    Kampfe, T.
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    Hanisch, N.
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    Biedermann, K.
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    Rudolph, M.
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    Brackmann, V.
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    Sanctis, C.
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    Jank, M.
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    Seidel, K.
    Thin-film transistors (TFTs) based on amorphous indium-gallium-zinc-oxide (a-IGZO) have attracted vast attention for use in organic light-emitting diode (AMOLED) displays due to their high electron mobility and large current on off ratio. Although amorphous oxide semiconductors show considerably less threshold voltage (Vth) variation than poly-silicon, large-area processing and degradation effects can impede the characteristic parameters of a-IGZO TFTs, which manifests in an uneven brightness distribution across the display panel. Such Vth variations are usually reduced by additional compensation circuits consisting of TFTs and capacitors. Herein, a new approach to compensate such variabilities is demonstrated: the integration of a programmable ferroelectric (FE) film in the gate stack o f the TFT. This simplifies the complexity of the pixel cell and potentially minimizes the need for compensation circuits, which is crucial for transparent displays. To test this new approach, fully integrated FE-TFTs (i.e., with vias contacting a structured bottom gate electrode from the top) based on a-IGZO and FE hafnium-zirconium oxide (HZO) are developed. A single low-temperature post-fabrication treatment at 350 °C for 1 h in air is used to simultaneously crystallize the HZO film in the FE phase and to reduce the number of defects in the a-IGZO channel. The structural and electrical characterizations provide comprehensive guidance for the design of effective FE-TFT gate stacks and device geometries. An accurate control of the polarization state and linear switching between multiple intermediate states is shown by using programming pulses of various amplitudes and widths. Furthermore, a direct correlation between the channel length and the applied pulse width for programming is observed.
  • Publication
    Improved electrical behavior of ZrO2-based MIM structures by optimizing the O3 oxidation pulse time
    ( 2015)
    Paskaleva, A.
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    Weinreich, W.
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    Bauer, A.J.
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    Lemberger, M.
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    Frey, L.
    The influence of oxidation pulse during atomic layer deposition (ALD) process on electrical and dielectric properties of metal-insulator-metal (MIM) structures with different ZrO2-based (e.g. pure ZrO2, Al- and Si- doped ZrO2) high-k dielectrics and different thicknesses has been investigated. Strongly pulse-time dependent as well as independent phenomena are observed and their thorough analysis has given more insight on the processes taking place in these structures thus allowing further optimization of their electrical performance. Longer oxidation pulses produce films with larger thicknesses which may be related to the incorporation of excess oxygen in the layers and the formation of less dense films. Incorporation of Al and 10 s pulse time are the most beneficial and provide structures with the lowest leakage current. At high positive voltages a significant increase of current and a change of I-V curve shape with increasing pulse time have been observed. The possible processes which provoke this change have been discussed. The analysis of leakage current mechanisms reveals that neither incorporation of Al or Si in ZrO2 nor oxidation pulse time change the energy position of traps participating in the conduction process, hence the nature of these traps remains unaffected - it is a single positively charged oxygen vacancy in ZrO2. The oxidation pulse time of 5-10 s is the optimal one which provides structures fulfilling the requirements for next generation MIM-based dynamic random access memories (DRAMs).
  • Publication
    Detailed leakage current analysis of metal-insulator-metal capacitors with ZrO2, ZrO2/SiO2/ZrO2, and ZrO2/Al2O3/ZrO2 as dielectric and TiN electrodes
    ( 2013)
    Weinreich, W.
    ;
    Shariq, A.
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    Seidel, K.
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    Sundqvist, J.
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    Paskaleva, A.
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    Lemberger, M.
    ;
    Bauer, A.J.
    ZrO2-based metal-insulator-metal capacitors are used in various volatile and nonvolatile memory devices as well as for buffer capacitors or radio frequency applications. Thus, process optimization and material tuning by doping is necessary to selectively optimize the electrical performance. The most common process for dielectric fabrication is atomic layer deposition which guarantees high conformity in three dimensional structures and excellent composition control. In this paper, the C-V and J-V characteristics of ZrO2 metal-insulator-metal capacitors with TiN electrodes are analyzed in dependence on the O3 pulse time revealing the optimum atomic layer deposition process conditions. Moreover, a detailed study of the leakage current mechanisms in undoped ZrO2 compared to SiO2- or Al2O3-dope d ZrO2 is enclosed. Thereby, the discovered dependencies on interfaces, doping, layer thickness, and crystalline phase's enable the detailed understanding and evaluation of the most suitable material stack for dynamic random access memory devices below the 20 nm generation.
  • Publication
    Structural properties of as deposited and annealed ZrO2 influenced by atomic layer deposition, substrate, and doping
    ( 2013)
    Weinreich, W.
    ;
    Wilde, L.
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    Müller, J.
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    Sundqvist, J.
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    Erben, E.
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    Heitmann, J.
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    Lemberger, M.
    ;
    Bauer, A.J.
    Thin ZrO2 films are of high interest as high-k material in dynamic random access memory (DRAM), embedded dynamic random access memory, and resistive random access memory as well as for gate oxides. Actually, ZrO2 is predicted to be the key material in future DRAM generations below 20 nm. Profound knowledge of pure and doped ZrO2 thin films, especially of the structural properties, is essential in order to meet the requirements of future devices. This paper gives a detailed overview about the structural properties of ZrO2 films in dependence of various process parameters. The study of atomic layer deposition (ALD) growth mechanisms of ZrO2 on a TiN-substrate in comparison to a Si-substrate covered with native oxide exhibits significant differences. Furthermore, the structural properti es crystallinity, surface roughness, and film stress are studied after the ALD deposition in dependence of the process parameters deposition temperature, layer thickness, and underlying substrate. Remarkable dependencies of the ZrO2 crystallization temperatures on the substrates are figured out. The structural properties after various annealing steps are monitored as well. The influence of doping by SiO2 and Al2O3 is studied, which is primarily used to keep the thin films amorphous during deposition.