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Well-known for its brake system components, e.g., the vacuum pump for brake systems, HELLA develops a digitally controlled actuator for brake-by-wire applications with a small design environment, high dynamics, and extended diagnostic functionality. Besides the functionalities in the brake system like ABS or EPB, the actuator can also provide Park Brake Actuator functionalities in a vehicle system.

The paper reports on the characterization of bipolar resistive switching materials and their integration into nanocrossbar structures, as well as on different memory operation schemes in terms of memory density and the challenging problem of sneak paths. TiO2, WO3, GeSe, SiO2 and MSQ thin films were integrated into nanojunctions of 100×100 nm2. The variation between inert Pt and Cu or Ag top electrodes leads to valence change (VCM) switching or electrochemical metallization (ECM) switching and has significant impact on the resistive properties. All materials showed promising characteristics with switching speeds down to 10 ns, multilevel switching, good endurance and retention. Nanoimprint lithography was found to be a suitable tool for processing crossbar arrays down to a feature size of 50 nm and 3D stacking was demonstrated. The inherent occurrence of current sneak paths in passive crossbar arrays can be circumvented by the implementation of complementary resistive switching (CRS) cells. The comparison with other operation schemes shows that the CRS concept dramatically increases the addressable memory size to about 1010 bit.

On the road towards higher memory density and computer performance, a significant improvement in energy efficiency constitutes the dominant goal in future information technology. Passive crossbar arrays of memristive elements were suggested a decade ago as non-volatile random access memories (RAM) and can also be used for reconfigurable logic circuits. As such they represent an interesting alternative to the conventional von Neumann based computer chip architectures. Crossbar architectures hold the promise of a significant reduction in energy consumption because of their ultimate scaling potential and because they allow for a local fusion of logic and memory, thus avoiding energy consumption by data transfer on the chip. However, the expected paradigm change has not yet taken place because the general problem of selecting a designated cell within a passive crossbar array without interference from sneak-path currents through neighbouring cells has not yet been solved satisfactorily. Here we introduce a complementary resistive switch. It consists of two antiserial memristive elements and allows for the construction of large passive crossbar arrays by solving the sneak path problem in combination with a drastic reduction of the power consumption.

We demonstrate the fabrication of a 3D memory architecture based on the resistive switching effect. Resistive memory (RRAM) is under wide investigation since it is non-volatile, promises fast operation and can be integrated into high density architectures like crossbar arrays. Here, silver-doped methyl-silsesquioxane (MSQ) is integrated in crossbar array structures for the following reasons. First, the material at the same time provides good planarization properties so that emerging lithography techniques like nanoimprint lithography (NIL) are applicable. Second, we could prove that silver-doped MSQ can be used as resistive switching material on the nano scale. Using this technique, crossbar arrays with a minimum feature size of only 100 nm are stacked on each other and the functionality is proved by electrical characterization. This comprises the doubling of the memory density and furthermore even higher integration is in principle not limited by this technique, while the CMOS overhead increases only slightly.

We report on the fabrication and the electrical characterization of platinum interconnects for novel non-volatile memory technologies. These nanowires present an important and essential contribution to the deep nanometer scaling of alternative architectures beyond CMOS, e.g. nanocrossbar arrays with resistance switching junctions. The nanowires, which have a thickness of 25nm and a width ranging from 200nm down to 40nm, were patterned using electron beam direct writing. They were deposited by UHV electron beam evaporation in combination with a lift-off process. The electrical characteristic is increasingly affected by the contribution of surface effects like scattering at grain boundaries and scattering at the surfaces as the wire dimensions become smaller. With decreasing width of the platinum wire an increasing resistivity was observed, which is consistent with the theories of Fuchs-Sondheimer and Mayadas-Shatzkes. Our studies have shown that the investigated structures possess a high stability concerning the operational current densities up to 4x10^7A/cm^2, and an additional annealing step results in an improvement of the electrical wire properties, which is explained by a higher quality of the grain boundaries and side walls.

Transparent polymers are considered as alternative low-cost mold materials in UV nanoimprint lithography (UV-NIL). Here, we demonstrate a nanoimprint process with molds made of rigid polymers novel for this application. These polymer molds are found to show high performance in the patterning with UV-NIL. Sub-50nm structures were fabricated with this process.

This paper focuses on the deposition and electromechanical characterization of lanthanum-doped lead hafnate titanate (PLHT) thin films as key material in piezoelectric microelectromechanical systems (pMEMS). PLHT (x/30/70) and PLHT(x/45/55) films with a thickness between 150 nm and 250 nm were deposited by chemical solution deposition (CSD). Thereby x varies between 0 and 10% La content. The electrical characterization shows that undoped (x=0) PLHT exhibit ferroelectric behavior similar to PZT of the same composition. La doping results in reduced ferroelectric properties and also affects the electromechanical properties. Measurements using a double beam laser interferometer yield a piezoelectric coefficient d 33 of 60 pm/V, which stays constant with an increasing electric field. This leads to a linear displacement compared to undoped PLHT or conventional PZT films used for MEMS applications.

We report on the deposition of Pb(Zrx,Ti1 - x)O3 (PZT) thin films by chemical solution deposition (CSD) on stainless steel foils. The electrical characterization proves good ferroelectric properties with a remnant polarization of 38 μ C/cm2. Since PZT is also piezoelectric the 35 μ m and 50 μ m thick metal foils are used to make piezoelectric actuated cantilever beams of several millimeter lengths. Actuated with 10–30 V a displacement up to 32 μ m was measured in quasi-static mode. In resonance mode the displacement increases several times at the same driving voltage.

In the field of microwave applications, microelectromechanical systems (MEMS) are attractive devices in order to force miniaturization by on chip integration. Here, we describe the design, fabrication and testing of a silicon based micromachined switch using piezo-electrically actuated elements. The microwave circuit consists of a coplanar waveguide (CPW) design with two piezoelectric activated beams integrated between the middle line and the ground planes. During operation the beams short the CPW by two overhanging bridge contacts and therefore the transmission characteristics of the microwave circuit change. The CPW is realized by 3 µm thick electroplated copper to yield good transmission characteristics, whereas the clamped—clamped beams benefit from a 250 nm thin PZT film between 100 nm thin Pt electrodes on top of a SiO2 layer. By the use of double side clamped beams awkward stress compensation of the piezoelectric stack is omitted. Instead the system relies on some initial mechanical stress. Measurements prove deflections of more than 13 µm for a 1400 µm long beam with operation voltages below 10 V. This is in good agreement with finite element simulations. The novel RF-MEMS is predicted to reach an isolation (in “on” state) of more than 20 dB up to 15 GHz.

This paper reports a new concept for microelectromechanical switches, which addresses high frequency requirements and is based on piezoelectric thin film actuation. Key issues are an improved stress compensation by using a double side suspended bridge structure, the electrical separation between actuation and high frequency part, electroplating of freestanding copper contacts and the appliance of surface silicon micromachining. Laser vibrometer measurements reveal a displacement up to 13 μ m at voltages below 10 V and resonant frequencies up to 100 kHz, depending on the length of the bridges.

Integrated RF-switches based on microelectromechanical systems (MEMS) promise a better performance than conventional devices. The employment of the piezoelectric effect allows a significant reduction of the device supply voltage compared to charge based actuator devices. This work presents the development and fabrication of lead-zirconate-titanate (PZT) actuated microswitches consisting of cantilevers and RF compatible contacts using chemical solution deposition (CSD) and surface micromachining. Measurements prove a possible “off-distance” of more than 20 μ m.

The effects of a decreasing top electrode size on the electric and piezoelectric properties of tetragonal Pb(Zr-X, Ti1-X)O-3 thin films are investigated. The effective piezoelectric small-signal coefficient d(33,eff) and the piezoelectric large signal-strain S are measured using a double-beam laser interferometer. Both properties are found to decrease rapidly with decreasing size of the used Pt top electrode for the investigated dimensions of 5 mm to 100 mum edge length (square pads). While the loss of d(33,eff) is as high as 75%, the influence on the relative permittivity is only small. The source of the pad size effect on the measured piezoelectric properties is found to be the mechanics of the layered structure commonly used for piezoelectric measurements (Pt/PZT/Pt/TiO/SiO2/Si), [PZT, Pb(Zr-x, Ti1-x)O-3] which is verified by finite element simulations. (C) 2004 American Institute of Physics.

In this work we report on the investigation of the piezoelectric and ferroelectric properties of Pb(Zr,Ti)O3 (PZT) thin films with a composition of 45% zirconium and 55% titanium prepared by chemical solution deposition (CSD) regarding the major properties required in MEMS applications. Therefore we have measured the polarization and the piezoelectric coefficient d 33 and strain using a high-resolution double beam laser interferometer. We found that d 33 alike the strain is nearly independent of the sample thickness. To estimate the lifetime of MEMS we stressed the samples by applying switching and non-switching voltage pulses. In the non-switching case, no change of the material properties was observed whereas the use of switching voltage pulses resulted in a strong decrease of the piezoelectric properties and the polarization. Here we found a linear behavior between the material properties in the fatigued state and the sample thickness.

Memristive switches are promising devices for future nonvolatile nanocrossbar memory devices. In particular, complementary resistive switches (CRSs) are the key enabler for passive crossbar array implementation solving the sneak path obstacle. To provide logic along with memory functionality, “material implication” (IMP) was suggested as the basic logic operation for bipolar resistive switches. Here, we show that every bipolar resistive switch as well as CRSs can be considered as an elementary IMP logic unit and can systematically be understood in terms of finite-state machines, i.e., either a Moore or a Mealy machine. We prove our assumptions by measurements, which make the IMP capability evident. Local fusion of logic and memory functions in crossbar arrays becomes feasible for CRS arrays, particularly for the suggested stacked topology, which offers even more common Boolean logic operations such as and and nor .

Recently, the sneak-path obstacle in passive crossbar arrays has been overcome by the invention of complementary resistive switches (CRSs) consisting of two bipolar antiserially connected memristive elements. Here, we demonstrate the vertical integration of CRS cells based on Cu/SiO2/Pt bipolar resistive switches. CRS cells were fabricated and electrically characterized, showing high resistance ratios (Roff/Ron >; 1500) and fast switching speed (

Resistive switching materials attract high scientific interest as a candidate for potential next-generation non-volatile memories. Nano crossbar structures and single junctions down to 60x60nm^2 with integrated silver doped methyl-silsesquioxane (MSQ) as switching material are fabricated using UV nano imprint. Here silver doped MSQ with platinum top and bottom electrodes replaces the formerly used material stack with undoped MSQ between platinum bottom and silver top electrodes. The new material system yields advantages regarding the process temperature budget and therefore multiple crossbar arrays and electrode layers are possible in order to multiply the integration density by the number of crossbar layers.

The resistive switching properties of NiO-based memory cells were investigated utilizing test structures with a storage contact size of 150 nm in diameter. Two well defined stable resistance states with high OFF/ON ratios were achieved by unipolar operation. Detailed electrical characterizations with respect to nonvolatile memory applications reveal fast ( 1000 cycles) and retention tests up to 110 °C show excellent stability and indicate the competitive potential with respect to established nonvolatile memory devices.

Resistively switching materials are in the focus of investigations for use in next-generation non-volatile resistive random access memories (RRAM). Crossbar structures with integrated resistively switching spin-on glass were fabricated using UV nanoimprint lithography. 32x32 bit crossbar arrays with a half pitch of 50nm were achieved. The switching characteristic of our Pt/spin-on glass/Ag material stack was proved on 100x100nm^2 nanocells. It shows resistance switching behavior which is comparable to material systems where the formation and dissolution of metallic filaments through a porous matrix is assumed to be the responsible switching mechanism.

Crossbar structures with integrated methyl-silsesquioxane (MSQ) were fabricated by UV nanoimprint lithography. The sandwiched MSQ film was used for the planarization of the bottom electrodes' interface as well as for the realization of functional resistively switching crosspoint junctions. With our process, future nonvolatile crossbar memories with stacking and, thus, high integration density potential can be realized. Using MSQ as functional material additionally indicates an attractive opportunity because it is highly CMOS compatible. By programming word registers with different bit patterns, we demonstrate the potential of this crossbar architecture for future memory and logic applications.

Nanoimprint lithography (NIL) is used to realize next generation memory and logic devices. The simple device structure consists of a resistance switching material sandwiched between two metal nanoelectrodes. Bottom and top electrodes are aligned perpendicular to each other building a crossbar array structure. A significant advantage of these future devices in addition to its simplicity is the high integration density. Crossbar arrays with 200nm electrodes and single cross junctions with 30nm electrodes were achieved using UV NIL. The bottom electrodes were embedded and planarized by spin on glass, such that an even surface for the realization of the top electrodes by UV NIL could be obtained. Finally electrical measurements demonstrated the function of the fabricated devices.

Currently, there is great interest in using solid electrolytes to develop resistive switching based nonvolatile memories (RRAM) and logic devices. Despite recent progress, our understanding of the microscopic origin of the switching process and its stochastic behavior is still limited. In order to understand this behavior, we present a statistical "breakdown" analysis performed on Cu doped Ge0.3Se0.7 based memory devices under elevated temperature and constant voltage stress conditions. Following the approach of electrochemical phase formation, the precursor of the "ON resistance switching" is considered to be nucleation - the emergence of small clusters of atoms carrying the basic properties of the new phase which forms the conducting filament. Within the framework of nucleation theory, the observed fluctuations in the time required for "ON resistance switching" are found to be consistent with the stochastic nature of critical nucleus formation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3631013]

In this report, the fabrication and electrical characterization of fully vertically integrated complementary resistive switches (CRS), which consist of two anti-serially connected Cu-SiO2 memristive elements, is presented. The resulting CRS cells are initialized by a simple procedure and show high uniformity of resistance states afterwards. Furthermore, the CRS cells show high switching speeds below 50 ns, making them excellent building blocks for next generation non-volatile memory based on passive nanocrossbar arrays.

Next generation memory materials and novel memory architectures are in the focus of investigations because CMOS based systems are supposed to reach their physical limits during the next decade. To enhance the potential for very high integration density we fabricated multilayer crossbar memory architectures with integrated spin-on glass (methyl-silsesquioxane - MSQ). UV nanoimprint lithography, a widely proposed future technology, was used to structure down to 100 nm feature sizes. Electrical measurements on silver doped MSQ devices show the potential for the use of the material composition in the field of future memory applications.

The storage principal of the Electrochemical Metallization Memory Cell is based on change of cell resistance induced by electro-chemical driven growth and rupture of a cupric or silver filament in an insulating matrix. This kind of switching was found in several materials as AgGeSe, CuGeS, silicon oxide or tungsten oxide [1].During write operation copper or silver is oxidized at the corresponding electrode and copper or silver ions are driven out of the copper or silver anode into the insulating matrix due to the applied field, whereas the insulating matrix serves as solid electrolyte. The silver or copper ions migrate towards the cathode. At the cathode electrochemical reduction occurs, and deposition of metallic copper or silver takes place. Fast diffusion paths in the solid electrolyte matrix or preferred nucleation sites (seeds) at the boundary lead to filamentary growth. This growing cupric or silver dendrite finally reaches the anode and switches the device to a low resistance state.Based on this switching mechanism a FEM simulation model was set up. To simplify the model space charges due to silver or copper migration are neglected. It is further assumed, that the conductivity in the solid electrolyte is only ionic. Hence, it is sufficient to solve the well-known Laplace equation to address the electric properties as well as ion migration. A “Level Set” method is used to track the boundary of the growing filament. The velocity of this boundary is proportional to the ionic current density calculated by Laplace equation. Based on this model simulations are applied to cell structures with multiple fast diffusion paths and seeds. Simulation results show that just one filament reaches the anode.In a second step, Butler-Vollmer boundary conditions are introduced. This nonlinearity leads to an exponential dependence between switching time and switching voltage. As switching voltage increases, switching time decreases.A simulation model capable of simulating ECM memory cells is presented. The model enables to simulate the behaviour of different cell geometries or different materials as solid electrolyte. Furthermore it gives deeper insight into the switching mechanism.This work was supported by the European project EMMA “Emerging Materials for Mass storage Architectures” (FP6-033751).

We report on the low resistance state (LRS) stability analysis of Ge0.3Se0.7 based solid electrolyte nonvolatile memory cells under elevated temperature and bias current stress conditions. The activation energy was found to be about 1.02 eV, which is comparable to that of an electromigration-induced failure process. Experimental results also show that there is trade-off between the LRS stability and the thickness of Ge0.3Se0.7 layer.

We present a fast and flexible method for the fabrication of nano-crossbar arrays with a feature size of 100 nm. TiO2 is integrated and electrically characterized as the nonvolatile resistively switching material. This structure serves as a key component for the investigation of novel high density nonvolatile resistive RAM cores.

While materials with a linear IV-characteristic yield in a practically unusable voltage swing when used in crossbar arrays, materials with a nonlinear IV-curve were expected to yield better results. With a fundamental analytical approach, we can show that the gain is theoretically limited to the square root of the number of word lines used in the crossbar. Furthermore the degree of nonlinearity must not exceed a certain value, otherwise the voltage swing decreases. TiO2 with its nonlinear IV-characteristic outperforms any possible material with a linear IV-characteristic but the voltage swing for large crossbars is still below 10%VDD and would demand for high costly sense amplifiers.

A novel dual-layered electrolytic resistance memory is proposed and its high retention ability at room and elevated temperature is successfully demonstrated. This dual-layered memory cell was fabricated as cross-point structure with active material, Cu containing Ge0.3Se0.7 based solid electrolyte and a thin insulator layer stack, sandwiched between an inert Pt bottom electrode and an oxidizable Cu top electrode. The reduction of the cell programming current up to few nA achieved with this dual- layered memory cell is promising for low power consumption applications.

We present the fabrication method and the electrical performance of nanoscale crosspoint junctions for two different metal/ oxide/ metal configurations. 100 × 100 nm2 small cells were fabricated by e-beam lithography and nanoimprint lithography (NIL), respectively. The electrical results show switching speeds of less than 10 ns for the SET and RESET operations, and resistance changes of several orders of magnitude. Additionally, the resistance state of TiO2 thin films reveal a strong dependence on the switch signal and demonstrates a retention time of up to 105 s at room temperature and 85°C. The tested materials and fabrication steps are in good accordance with current and future CMOS technology and provide a way to achieve low cost, high density non-volatile memory.

The fatigue of the electromechanical properties of tetragonal PbZrx, Ti1-xO3 thin films is investigated. The decrease of electromechanical small-signal response is compared to the fatigue of the electric properties and examined in detail. Property fatigue is attributed mainly to switching-failure of the unit cells. (C) 2005 American Institute of Physics.

The effects of an increasing small signal amplitude on the piezoelectric small-signal response and electrostriction of tetragonal Pb(Zr-x, Ti1-x)O-3 thin films are investigated. The piezoelectric small-signal coefficient d(33), piezoelectric large signal-strain S, and electrostriction coefficient M-33 are measured using a double-beam laser interferometer. A continuously increasing influence of the small signal amplitude is found starting at very low values. In particular, the impact on the measured coercive field E-c is found to be stronger than the impact of the cycling frequency of the applied bias field. Also, unexpected electrostrictive behavior is investigated and explained by the influence of ferroelectric switching on the intrinsic piezoelectric lattice strain. Furthermore, the influence of an applied small-signal on the piezoelectric large-signal response is investigated. (C) 2004 American Institute of Physics.

An evolution of the double-beam laser interferometer used for piezoelectric measurements in ferroelectric thin films is reported. Measuring the d(33) hysteresis of a ferroelectric material using lock-in technique with large time constants requires a varying bias field to be applied to the sample over a long period of time. This long-term application leads to electrical stress during the measurement. We present a measurement technique using a different source for the applied field and a varied method for averaging the interferometric response. The measurement time for a complete d(33) hysteresis will be shortened down to several seconds. Also, the cycle frequency becomes comparable to electrical hysteresis measurements. Experimental results on quartz and Pb(Zr-(X),Ti(1-X))O-3 are given to demonstrate the capabilities of the interferometer and the new measurement method. (C) 2003 American Institute of Physics.

Piezoelectric and electrostrictive materials are potential candidates for integrated micro systems. They can be used in cantilever laminated structures for different applications, e.g. active vibration control or agile transducers [1-3]. Due to the necessity of miniaturization of MEMS devices and the reduction of process costs and time, the use of chemical solution deposition (CSD) technique with microlithography and reactive ion etching (RIE) are essential.Within this work we used these techniques in combination with silicon bulk micro machining technique to fabricate piezoelectric Pb(Zr,Ti)O3 (PZT) and electrostrictive Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT) coated micro cantilevers with different lengths which can be used in micro switch or micro mirror applications. In general PMN shows no elastic hysteresis and a better aging behavior than PZT ceramics. Since the electrostrictive effect is smaller than the piezoelectric effect the tip deflection of PMN-PT coated beams is much lower. Cantilevers with two ceramic thin film layers and an internal electrode (bimorph) were designed and compared to such with single ceramic thin film layers (monomorph). For fabrication control and electrical characterization SEM, polarization hysteresis-, and CV-measurements were performed. Laser interferometry measurements were used to characterize the electromechanic performance of the ceramic thin films and cantilevers.

Aerosol Jet® Printing is investigated as deposition technique for silicon as anode material for lithium-ion batteries. Binder free structures with silicon particles were deposited and galvanostaticly cycled. The morphological changes of the electrode were examined with SEM, Raman spectroscopy and x-ray photon spectroscopy (XPS). The fast degradation is explained with the huge amount of side reactions building LiF and the low conductivity of the intrinsic silicon particles. The addition of conducting carbon did not affect cycling stability.

Nanostructured Pt/ TiO2 /Ti/Pt crosspoint junctions with lateral dimensions as small as 100×100 nm2 were prepared on silicon substrates by the use of nanoimprint lithography and reactive ion etching to structure the metal electrodes combined with atomic layer deposition of the resistive switching TiO2 layer. A thickness of the amorphous TiO 2 films of only 8 nm already led to functioning nanocrosspoint structures with respect to resistance switching behavior. As-prepared structures exhibited very high-resistance states with diodelike I-V characteristics. After a negative-current-driven electroforming step, the devices could be repeatably switched between two stable states. The switching characteristics were found to depend strongly on the resistance state after the electroforming procedure. Low resistance values around 1 k led to high current switching, and resistances of about 10 k led to low current switching. Furthermore, multilevel switching was demonstrated by the use of 10 and 50 ns set voltage pulses.

The ultimate sensitivity of any solid state device is limited by fluctuations. Fluctuations are manifestations of the thermal motion of matter and the discreteness of its structure which are also inherent ingredients during the resistive switching process of resistance random access memory (RRAM) devices. In quest for the role of fluctuations in different memory states and to develop resistive switching based nonvolatile memory devices, here we present our study on random telegraph noise (RTN) resistance fluctuations in Cu doped Ge0.3Se0.7 based RRAM cells. The influence of temperature and electric field on the RTN fluctuations is studied on different resistance states of the memory cells to reveal the dynamics of the underlying fluctuators. Our analysis indicates that the observed fluctuations could arise from thermally activated transpositions of Cu ions inside ionic or redox "double-site traps" triggering fluctuations in the current transport through a filamentary conducting path. Giant RTN fluctuations characterized by relative resistance variations of up to 50% in almost macroscopic samples clearly point to the existence of weak links with small effective cross-sectional areas along the conducting paths. Such large resistance fluctuations can be an important issue for the industrial applications of RRAM devices because they might lead to huge bit-error rates during reading cycles.

The effects of reversible and irreversible switching processes on the electromechanical large-signal strain S of tetragonal Pb(Zrx,Ti1−x)O3 thin films are investigated and discussed. Starting from electric small- and large-signal measurements, the percentage of switched unit cells cesw is calculated. The result is then used in combination with the measured electromechanical field-induced small-signal response to calculate the field-induced large-signal strain S. Enhanced models for this calculation are developed improving a known model. Differences between the calculated and measured large-signal strains are discussed in respect to parameter influences and irreversible contributions. In addition, detailed insight on the switching processes in respect to the electromechanical properties is given.