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Electrolyte-Gated Oxide Transistors by Ink-jet Printing

Printed electronics is a rapidly developing field of research that involves solution processing and covers a broad range of research activities, starting from a basic field-effect transistor to complex logics, memories, lighting, photovoltaics and sensors.

Printed logics is the most complex and intriguing part of it. In order to fulfill the promise of large area devices on inexpensive substrates, such as paper, plastic etc., it is essential to limit the process temperature to lowest possible values. Consequently, organic materials have traditionally been used, although long-term stability and device mobility were always been the issues of concern. Inorganic materials, e.g., oxide semiconductors, on the other hand, show much superior electrical performance once they are processed at high temperatures. However, a reduction in the process temperature drastically reduces the device performance. This problem can be circumvented by suitable changes in the materials, the inner-lying chemistry or even the device architecture. Research focus in the group now, is to find solutions through these routes so as to reduce the process temperature while keeping the device performance at the same level as high temperature processed electronics.


Group members (left to right): Horst Hahn, Gabriel Marques, Jasmin Aghassi, Ben Breitung, Robert Kruk, Tessy Baby, Surya Singaraju, Parvathy Sukkurji


To carry this forward, in the printed electronics group at Institute of Nanotechnology we focus on the fundamental issues concerning solution-processed/ printed oxide electronics.

One key aspect of our research is that we concentrate on electrolyte-gating approach to ensure extremely high gating efficiency even with oxide semiconductors which when solution-processed usually result large interface/ surface roughness, thereby reducing the dielectric efficiency/ polarizability. However, our composite polymer electrolytes can easily follow any surface corrugation offered by the nanostructured oxide semiconductors towards a highly conformal semiconductor/ dielectric interface.

Equipments: INT boasts of a rich variety of equipment used for conducting nano-micro electronics research and to fabricate thin film electronics.

From spin coating to metal evaporators for deposition of thin films, from thermal box furnace to photonic curing instruments for thin film preparation; from X-ray diffractometers to X-ray photoelectron spectroscopy for material characterization; from atomic force microscopy to transmission electron microscopy for imaging and morphological studies; and a multitude of oscilloscopes and Keithley multimeters and Agilent probe station for electrical characterization, there is a huge scope for exciting research both within the printed electronics group and by cooperation with sub-groups at the Institute of Nanotechnology.


Cooperating Partnership:

MERAGEM: Graduate school for Printable Electronics in cooperation with Karlsruhe Institute of technology and Hochschule, Offenburg. The school is supported by the Ministry of Science, Research and Arts, Baden-Württemberg, Germany. The school has two coordinating professors and cooperation is spread from the Institute of Nanotechnology and Chair of Dependable Nano Computing at KIT and the Department of Electrical Engineering at Offenburg University of Applied Sciences.


In the news!

Ink‐Jet Printable, Chemically Crosslinked Ion‐Gel as Electrolyte for Thin Film Transistors

An ink‐jet printable, chemically crosslinked ion‐gel is fabricated by self‐assembled gelation. Poly(vinyl alcohol) and poly(ethylene‐alt‐maleic anhydride) are used as the polymer backbone and chemical crosslinker, respectively, and 1‐ethyl‐3‐methylimidazolium trifluoromethanesulfonate ([EMIM][OTf]) is utilized as an ionic species. The ion‐gel exhibits an ionic conductivity of ≈5 mS cm−1 and an effective capacitance of 5.4 µF cm−2 at 1 Hz.

Adv Mat. Int., 2019, 6 (21), pp 1901074
Development of Fully Printed Electrolyte-Gated Transistors with Graphene Passives

The work involves the fabrication of a graphene passive structure based electrolyte gated oxide transistor. These fully printed transistors are highly reproducible and function at very low input voltages. The graphene electrodes offer high chemical stability and good electrical compatibility resulting in a high on/off current ratio, in the orders of 5.

ACS Appl. Elec. Mat., 2019, 1 (8), pp 1538–1544

Progress Report on “From Printed Electrolyte‐Gated Metal‐Oxide Devices to Circuits”

Printed electrolyte‐gated oxide electronics is an emerging electronic technology in the low voltage regime (≤1 V). The low voltage is achieved by employing the advantages of solution processable, solid polymer electrolytes, or ion gels that provide high gate capacitances produced by a Helmholtz double layer. Herein, recent advances in building electronic circuits based on indium oxide, n‐type electrolyte‐gated transistors (EGTs) are studied. When integrated into ring oscillator circuits a digital performance ranging from 250 Hz at 1 V up to 1 kHz is achieved. Sequential circuits such as memory cells are also demonstrated in this work. More complex circuits are feasible but remain challenging also because of the high variability of the printed devices. However, the device inherent variability can be even exploited in security circuits such as physically unclonable functions (PUFs), which output a reliable and unique, device specific, digital response signal. As an overall advantage of the technology all the presented circuits can operate at very low supply voltages (0.6 V), which is crucial for low‐power printed electronics applications.












Figure 1.  a) Cross section of an Electrolyte-Gated Transistor. b) Optical image view of the EGFET. c) Transfer curve: the gate (Ig) and the drain–source (Ids) currents are plotted against the gate–source voltage (Vgs) at different drain–source voltages (Vds) (denoted in the legend). d) Output curve: drain–source current (Ids) versus the drain–source voltage at different gate–source voltages (Vgs).



Figure 2.  Performance of a three‐stage ring oscillator. a) Output voltage (Vout) versus the time at a supply voltage (Vdd) of 2.0 V and a frequency of 352 Hz. b) Frequency, c) current flow, d) power consumption, e) switching‐resistance (Rsw) and f) switching‐capacitance (Csw) of the three‐stage ring oscillator in dependence of the supply voltage (Vdd).


Learn more: Gabriel Marques et al. Adv Materials. 2019; 31 (26): 1806483

Digital power and performance analysis of inkjet printed ring oscillators based on electrolyte-gated oxide electronics

Printed systems spark immense interest in industry, and this has led to intense research to control variability; however, printed electrolyte-gated transistors (EGTs) and logics derived thereof still have not been sufficiently developed to be adapted by industry. One of the reasons for this is the lack of control of the threshold voltage during production. In this work, we show an approach to adjust the threshold voltage (Vth) in printed EGTs with high accuracy by doping indium-oxide semiconducting channels with chromium. Despite high doping concentrations achieved by a wet chemical process during precursor ink preparation, good on/off-ratios of more than five orders of magnitude could be demonstrated. The synthesis process is simple, inexpensive, and easily scalable and leads to depletion-mode EGTs, which are fully functional at operation potentials below 2 V and allows us to increase Vth by approximately 0.5 V.











Figure 1.Powder XRD patterns of the channels for 0–12.5% Cr:In2O3 (a) patterns in the range of 20° to 55°, and (b) magnification of the (222) reflexes in the range of 28° to 33° for better visibility of the shifts; reference pattern of In2O3: ICSD 169420.



 Figure 2. Values for Vth for all devices with insets as magnifications of the sets with 0 and 10% doping, respectively.


Learn more: Felix Neuper et al. ACS Omega. 4, 24, 20579-20585 (2019)

Sub-50 nm Channel Vertical Field-Effect Transistors using Conventional Ink-Jet Printing

A printed vertical field-effect transistor is demonstrated, which decouples critical device dimensions from printing resolution. A printed mesoporous semiconductor layer, sandwiched between vertically stacked drive electrodes, provides <50 nm channel lengths. A polymer-electrolyte-based gate insulator infiltrates the percolating pores of the mesoporous channel to accumulate charge carriers at every semiconductor domain, thereby, resulting in an unprecedented current density of MA cm−2.







Figure 1 a) System comprising the bottom drive electrode along with the printed metal–organic precursor ink that would form the mesoporous semiconductor layer upon annealing. b) After structuring and placing the top drive electrode. c) After the annealing process that removes the polymer and opens the pores; the porous semiconductor channel layer is now sandwiched between the drive electrodes. d) The final vFET geometry after printing the polymer electrolyte (gate dielectric)that covers the porous channel and the displaced gate electrode. e) SEM image showing the actual porous SnO2 surface morphology; the bright white phase represents the material and the dark regions show the pores. f) 3D surface rendering of the reconstructed STEM tomography showing the 3D structure of SnO2. All the images were generated from the sample annealed at 550 °C for 5 min.

Learn more: Tessy. Baby et al., Advanced Materials, 29 (4), 2017, 1603858

Most Recent Publications

Development of Fully Printed Electrolyte-Gated Oxide Transistors Using Graphene Passive Structures.
Singaraju, S. A.; Baby, T. T.; Neuper, F.; Kruk, R.; Aghassi-Hagmann, J.; Hahn, H.; Breitung, B.
2019. ACS applied electronic materials, 1 (8), 1538–1544. doi:10.1021/acsaelm.9b00313
Tailoring Threshold Voltages of Printed Electrolyte-Gated Field-Effect Transistors by Chromium Doping of Indium Oxide Channels.
Neuper, F.; Chandresh, A.; Singaraju, S. A.; Aghassi-Hagmann, J.; Hahn, H.; Breitung, B.
2019. ACS omega, 4 (24), 20579–20585. doi:10.1021/acsomega.9b02513
Ink‐Jet Printable, Self‐Assembled, and Chemically Crosslinked Ion‐Gel as Electrolyte for Thin Film, Printable Transistors.
Jeong, J.; Marques, G. C.; Feng, X.; Boll, D.; Singaraju, S. A.; Aghassi‐Hagmann, J.; Hahn, H.; Breitung, B.
2019. Advanced materials interfaces, 6 (21), 1901074. doi:10.1002/admi.201901074
Reversible control of magnetism: On the conversion of hydrated FeF3 with Li to Fe and LiF.
Singh, R.; Witte, R.; Mu, X.; Brezesinski, T.; Hahn, H.; Kruk, R.; Breitung, B.
2019. Journal of materials chemistry / A, 7 (41), 24005–24011. doi:10.1039/c9ta08928d
Influence of Humidity on the Performance of Composite Polymer Electrolyte-Gated Field-Effect Transistors and Circuits.
Marques, G. C.; Von Seggern, F.; Dehm, S.; Breitung, B.; Hahn, H.; Dasgupta, S.; Tahoori, M. B.; Aghassi-Hagmann, J.
2019. IEEE transactions on electron devices, 66 (5), 2202–2207. doi:10.1109/TED.2019.2903456