Scanning laser lithography is a maskless method for exposing photoresist during semiconductor manufacturing. In this method, the energy of a focused beam is controlled while scanning the beam or substrate. With a positive photoresist material, areas that receive an exposure dosage over the threshold energy are dissolved during development. The surface dosage is related to the exposure profile by a convolution and nonlinear function, so the optimal exposure profile is nontrivial. A gradient-based optimization method for determining an optimal exposure profile, given the desired pattern and models of the beam profile and photochemistry, is described. This approach is more numerically efficient than optimal barrier-function-based methods but provides near-identical results. This is demonstrated through simulation and experimental lithography.
KEYWORDS: Photoresist materials, Coating, Absorption, 3D modeling, Optical lithography, Near field scanning optical microscopy, Computer simulations, Near field optics, Lithography, Aluminum
This article describes two- and three-dimensional optical simulations for determining optimal conditions for near-field scanning optical lithography. It was found that a combination of 30-nm thick photoresist and 50-nm thick anti-reflective coating will yield optimal results with 405 nm incident light and a hollow-cantilever probe with 100-nm aperture width. In addition to identifying the optimal conditions, the sensitivity of the resolution with respect to each parameter is explored and plotted. The mechanisms behind each trend are described with supporting simulation data.
Due to their high stiffness, small dimensions and low mass, piezoelectric stack actuators are capable of developing
large displacements with bandwidths of greater than 100 kHz. However, due to their large electrical capacitance,
the associated driving amplifier is usually limited in bandwidth to a few kHz.
In this paper the limiting characteristics of piezoelectric drives are identified as the signal-bandwidth, output-impedance,
cable inductance, and power dissipation. A new dual-amplifier is introduced that exhibits a bandwidth
of 2 MHz with a 100 nF capacitive load. Experiments demonstrate a 20 V 300 kHz sine wave being applied
to a 100 nF load with negligible phase delay and a peak-to-peak current of 3.8 A. Although the peak output
voltage and current is 200 V and 1.9 A, the worst-case power dissipation is only 30 W.
KEYWORDS: Smart structures, Actuators, Control systems, Sensors, Systems modeling, Signal attenuation, Control systems design, Vibration control, Transducers, Bandpass filters
This paper introduces a simple and robust technique for vibration control in smart structures with collocated
sensors and actuators. The technique is called Integral Resonant Control (IRC). We show that by adding a
direct feed-through to a collocated system, the transfer function can be modified from containing resonant poles followed by interlaced zeros, to zeros followed by interlaced poles. This structure permits the direct application of integral feedback and results in good stability and damping performance. To alleviate the problems due to unnecessarily high controller gain below the first mode, a slightly complicated second-order controller is also discussed. A piezoelectric laminate cantilever beam used to test the proposed control scheme exhibits up to 24 dB modal damping over the first eight modes.
Low-frequency reverberant sound fields are usually suppressed by means of either adaptive feedforward control
or Helmholtz resonator. In this paper, an electrical impedance is connected to the terminals of an acoustic
loudspeaker, the mechanical dynamics, and hence acoustic response can be made to emulate a sealed acoustic
resonator. No microphone or velocity measurement is required. In some cases, the required electrical circuit is
simply the parallel connection of a capacitor and resistor. Experimental application to a closed acoustic duct
results in 14 dB pressure attenuation of a single acoustic mode.
By attaching an electromagnetic transducer to a mechanical isolation system and shunting the terminals of the transducer with electrical impedance, we can provide improved isolation performance while eliminating the need for an additional sensor. Simulated and experimental results on a simple electro-mechanical isolation system show that the proposed controller is capable of peak damping and high frequency attenuation.
Piezoelectric transducers are commonly used as strain actuators in the control of mechanical vibration. One control strategy, termed piezoelectric shunt damping, involves the connection of an electrical impedance to the terminals of a structurally bonded transducer. Many passive, non-linear, and semi-active impedance designs have been proposed that reduce structural vibration. This paper introduces a new technique for the design and implementation of piezoelectric shunt impedances. By considering the transducer voltage and charge as inputs and outputs, the design problem is reduced to a standard linear regulator problem enabling the application of standard synthesis techniques such as LQG, H2, and Hinf. The resulting impedance is extensible to multi-transducer systems, is unrestricted in structure, and is capable of minimizing an arbitrary performance objective. An experimental comparison to a resonant shunt circuit is carried out on a cantilevered beam. Previous problems such as ad-hoc tuning, limited performance, and sensitivity to variation in structural resonance frequencies are significantly alleviated.
This paper introduces a new multiple mode passive piezoelectric shunt damping technique. The robust passive piezoelectric shunt controller is capable of damping multiple structural modes and maybe less susceptible to variations in environmental conditions that can severely effect the performance of other controllers. The proposed control scheme is validated experimentally on a piezoelectric laminated plate structure.
This paper introduces electromagnetic shunt damping (EMSD) which is similar to piezoelectric shunt damping. EMSD has four major advantages over piezoelectric shunt damping; simple transducer manufacturing, smaller shunt voltages, long stroke and larger control forces. A novel single mode shunt control strategy is validated through experimentation on a simple electromagnetic mass spring damper system. Theoretical results are also presented.
KEYWORDS: Transducers, Signal processing, Inductance, Digital signal processing, Switching, Actuators, Bridges, Resistors, Amplifiers, Ferroelectric materials
Passive shunt damping involves the connection of an electrical shunt network to a structurally attached piezoelectric transducer. In recent years, a large body of research has focused on the design and implementation of shunt circuits capable of significantly reducing structural vibration. This paper introduces an efficient, light weight, and small-in-size technique for implementing piezoelectric shunt damping circuits. A MOSFET half bridge is used together with a signal processor to synthesize the terminal impedance of a piezoelectric shunt damping circuit. Along with experimental results demonstrating the effectiveness of switched-mode shunt implementation, we discuss the design of a device aimed at bridging the gap between research in this area and practical application.
Piezoelectric transducers are known to exhibit less hysterisis when driven with current or charge rather than voltage. Despite this advantage, such methods have found little practical application due to the poor low frequency response of present current and charge driver designs. This paper introduces the compliance feedback current driver containing a secondary voltage feedback loop to prevent DC charging of capacitive loads and to compensate for any voltage or current offsets in the driver circuit. Low frequency bandwidths in the milli-Hertz range can be achieved.
This paper introduces a passive piezoelectric shunt controller, for damping multiple modes of a flexible structure using one piezoelectric transducer. The series-parallel impedance structure has a number of advantages over to previous techniques; it is simpler to implement, requires less passive elements and contains smaller inductors values. The vibration control strategy is validated through experimental work on a piezoelectric laminated cantilever structure.
KEYWORDS: Lithium, Lutetium, Digital signal processing, Erbium, Smart materials, Signal processing, Process control, Digital Light Processing, Palladium, Transducers
Piezoelectric shunt damping systems reduce structural vibration by shunting an attached piezoelectric transducer with an electrical impedance. Current impedance designs result in a coupled electrical resonance at the target modal frequencies. In practical situations, variation in structural load or environmental conditions can result in significant changes in the structural resonance frequencies. This variation can severely reduce shunt damping performance as the electrical impedance remains tuned to the nominal resonance frequencies. This paper introduces a method for online adaption of the shunting impedance. A reconstructed estimate of the RMS\ strain is minimized by varying the component values of a synthetic shunt damping circuit. The presented techniques are applied in real time, to tune the component values of a randomly excited beam.
A new multi-mode semi-active shunt technique for controlling vibration in piezoelectric laminated structures is proposed in this paper. The effect of the ``negative capacitor'' controller is studied theoretically and then validated experimentally on a piezoelectric laminated simply-supported beam. The negative capacitor controller is similar in nature to passive shunt damping techniques, as a single piezoelectric transducer is used to dampen multiple modes. While achieving comparable performance to that of the purely piezoelectric passive shunt schemes, the negative capacitor controller has a number of advantages. It is simpler to implement, less sensitive to environmental variations, and can act as a multiple mode and broadband vibration controller. Experimental resonant amplitudes for the piezoelectric laminated simply-supported beam 1st, 2nd, 3rd, 4th and 5th modes were successfully reduced by 6.1, 16.3, 15.2, 11.7 and 10.2dB.
Piezoelectric transducer (PZT) patches can be attached to a structure in order to reduce vibration. The PZT patches essentially convert vibrational mechanical energy into electrical energy. The electrical energy can be dissipated via an electrical impedance. Currently, impedance designs require experimental tuning of resistance values by minimizing the H2 norm of the damped system. After the design process, shunt circuits are normally implemented using discrete reasonable performance has been an ongoing and unaddressed problem in shunt damping. A new approach to implementing piezoelectric shunt circuits is presented. A synthetic impedance, consisting of a voltage controlled circuit source and DSP system, is used to synthesize the terminal impedance of a shunt network. A two mode shunt circuit is designed and implemented for an experimental simply supported beam. The second and third structural modes of the beam are reduced in magnitude by 22 and 18 dB.
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