Han-Jan Chen

Novel compact microstrip interdigital bandstop filters

A novel compact microstrip interdigital band-stop filter is designed and implemented. The structure is similar to that of an interdigital capacitor. The input port and output ports are connected to form the bandstop characteristic. This proposed filter with microstrip interdigital geometry not only exhibits good bandstop characteristics and a tunable central frequency, but it also is easy to fabricate and integrate. The features of this microstrip interdigital bandstop filter are smaller than those of the conventional bandstop filter. Simulation results closely correspond to the experiments.

Normal incidence intersubband optical transition in GaSb/InAs superlattices

A novel intersubband optical transition, incorporating interband and p‐type intersubband optical transition mechanisms, in a suitably designed GaSb/InAs superlattice is proposed. Such a structure utilizes the strong mixing of GaSb light‐hole band with InAs conduction band and the heavy‐hole to light‐hole intervalence‐subband transition in the GaSb/InAs superlattice to obtain a strong normal incidence photoabsorption coefficient (over 8.0×104 cm−1) at a wavelength near 10 μm.

Spurious suppression of a microstrip filter using three types of rectangular PBG loops

A novel microstrip bandpass filter with three types of rectangular, photonic bandgap (PBG) loops on a middle layer was designed and demonstrated using a full-wave electromagnetic (EM) simulator, with the predicted results verified by experiment. This investigation presents the configurations of conventional parallel-coupled 2 GHz filters with arid without a PBG. The middle-layer of PBG loops adds an extra stopband-rejection mode to filter stop-band; and it provides attenuation in excess of 25 dB at the second, third, and fourth harmonics, thus demonstrating that superior stopband characteristics at high frequency can be obtained using the proposed PBG loops in microwave filters.

A novel integrable surface acoustic wave notch filter

Abstract Although surface acoustic wave (SAW) notch filter was investigated in the past, the structures of these devices often needed the extra lumped-element such as resistance R , capacitance C , and inductance L so that the devices are complex and integrated hardly. From this, we offer a simple kind of the planar structure to the novel SAW notch filters that have smaller size and can be fabricated easily. We adopt the SAW and the interdigital transducer’s (IDT’s) theory to fabricate the SAW notch filter. In this paper, we use an IDT finger width 8 μm with conventional photolithography process, lift-off technique, and IDT electrode to fabricate on 128° rotated YX-cut lithium niobate (LiNbO 3 ). Finally, we get the frequency responses of the novel SAW notch filter with the center frequency 113.4 MHz, the 3 dB bandwidth 0.36%, and the insertion loss S 21 =−10.583 dB.

The negative differential resistance behavior in delta‐doped GaAs structure due to resonant interband tunneling

A GaAs delta‐doped tunneling diode having a δn+‐i‐δp+‐i‐δn+ structure is investigated. A negative differential resistance behavior with peak‐to‐valley ratio as high as 3.1 and a peak current density of 3 kA/cm2 is exhibited when the device is operated at room temperature. It becomes resistor‐like at the temperature of 77 K. Theoretical analysis, based on envelope wave function approximation, indicates that the resonant interband tunneling process is responsible for room‐temperature characteristics, while the band‐gap widening effect is responsible for low‐temperature behavior. Furthermore, the dependence of device performance on such structure parameters as doping level, and the physical dimension of the delta‐doped region, etc., is discussed, and found to agree well with experimental results.

Self-consistent simulation of modulation-doped field-effect transistors

Abstract Due to the fact that conventional linear charge-control modulation-doped field-effect transistor (MODFET) models assume full depletion in the doping layer, they are not able to model the nonlinear charge-control relation arising from neutralized donor effect near large gate bias. This neutralized donor effect, also called parasitic MESFET effect, saturates two-dimensional electron gas (2DEG) concentration and raises gate-source capacitance to make high frequency performance poor. In this paper, electron behavior of MODFET along the growth direction is numerically modeled through self-consistent calculation to achieve a more exact charge-control relation. Then, 2DEG channel mobility is described by a semi-empirical analytical form and substituted into a current-density equation together with the charge-control relation fitted by least-square polynomial in order to easily solve for drain-source current and gate transconductance. These theoretically calculated results are in good agreement with those experimental results presented in the literature.

An energy‐ and spatial‐dependent effective mass approach for resonant interband tunneling devices

A theoretical study of resonant interband tunneling in GaAs δ‐doped inducing homostructure and polytype GaSb/AlSb/InAs heterostructure is presented in this article. The resonant interband tunneling in such homo‐ and heterostructures is modeled by an energy‐ and spatial‐dependent effective mass equation incorporating the general transfer matrix method. The present formalism is based on the envelope function approximation as done to date, but contains two significant improvements: a more realistic treatment of the spatial and energy dependence of effective‐mass and bandstructures; and the avoidance of plane‐wave, Airy function or Wentzel–Kramers–Brillouin approximations for calculating the envelope function in favor of direct numerical evaluation. The transmission coefficients of the unipolar and bipolar resonant interband tunneling structures are calculated and the symmetric and asymmetric multiple quantum well resonant interband tunneling structures are also discussed.

The negative differential resistance behavior of GaAs delta-doped structures

Abstract In this work we analyzed the negative differential resistance (NDR) phenomenon of GaAs delta-doped structures by using the Airy function approach. Theoretical results indicate that the NDR behavior results from the resonant tunneling process in the delta-doped layer, which is further evidenced by the measured current-voltage characteristic of a Schottky- δn + -Schottky device. Our analysis method is useful for designing GaAs delta-doped devices.

Multilayer stepped-impedance resonator band-pass filter implementing using low temperature cofired ceramic structure

A tapped-line stepped-impedance resonator band-pass filter was implemented using a low temperature cofired multilayer-ceramic structure. By constructing a multilayer structure, a compact band-pass filter was realized. Moreover, the multilayer structure demonstrated an extra cross-coupling effect that produced extra transmission zeros in the stopband and, hence, realized a highly steep passband skirt. The center frequency of the fabricated band-pass filter was 6.075 GHz and the 3 dB fractional bandwidth was 18%. The measured insertion loss and return loss of the filter were -0.31 dB and -28 dB, respectively. The measured response of the fabricated band-pass filter was in good agreement with simulated results.

Factor considerations on the novel surface acoustic wave devices by using piezoelectric materials

Due to the increasing variety and capacity of information and communication media, systems of microwave band communication have branched out extensively. Surface acoustic wave (SAW) devices are commonly used in microwave applications, primarily because these devices can be fabricated by using photolithographic processes, and easily integrated into other passive and active devices. SAW devices have been successfully employed for various commercial applications, such as intermediate-frequency (IF) filters for televisions and radio-frequency (RF) filters for mobile telecommunications, using small size and mass-production fabrication processes. We apply the principles of surface acoustic wave and microwave theory, by properly designed circuit with cross-coupled combination, the conventional photolithography and lift-off technique were applied for metal pattern fabrication on the 128/spl deg/-rotated YX-cut LiNbO/sub 3/ piezoelectric material substrate.