A novel cascaded DFB laser,which consists of two serial gratings to provide selectable wavelengths,is presented and analyzed by the transfer matrix method.In this method,efficient facet reflectivity is derived from the transfer matrix built for each serial section and is then used to simulate the performance of the novel cascaded DFB laser through self-consistently solving the gain equation,the coupled wave equation and the current continuity equations.The simulations prove the feasibility of this kind of wavelength selectable laser and a corresponding designed device with two selectable wavelengths of 1.51μm and 1.53μm is realized by experiments on InP-based multiple quantum well structure.
Compared with BVcEo, BVcEs is more related to collector optimization and more practical significance, so that BVcEs × fT rather than BVcEo ×fT is employed in representing the limit of the product of the breakdown voltage-cutoff frequency in SiGe HBT for collector engineering design. Instead of a single decrease in collector doping to improve BVcEs × fT and BVcEo × fT, a novel thin composite of N- and P＋ doping layers inside the CB SCR is presented to improve the well-known tradeoff between the breakdown voltage and cut-off frequency in SiGe HBT, and BVCES and BVCEO are improved respectively with slight degradation in fTAs a result, the BVcEs × fT product is improved from 537.57 to 556.4 GHz.V, and the BVcEo ×fT product is improved from 309.51 to 326.35 GHz.V.
A method of non-uniform finger spacing is proposed to enhance thermal stability of a multiple finger power SiGe heterojunction bipolar transistor under different power dissipations. Temperature distribution on the emitter fingers of a multi-finger SiGe heterojunction bipolar transistor is studied using a numerical electro-thermal model. The results show that the SiGe heterojunction bipolar transistor with non-uniform finger spacing has a small temperature difference between fingers compared with a traditional uniform finger spacing heterojunction bipolar transistor at the same power dissipation. What is most important is that the ability to improve temperature non-uniformity is not weakened as power dissipation increases. So the method of non-uniform finger spacing is very effective in enhancing the thermal stability and the power handing capability of power device. Experimental results verify our conclusions.
An improved inductor layout with non-uniform metal width and non-uniform spacing is proposed to increase the quality factor（Q factor）.For this inductor layout,from outer coil to inner coil,the metal width is reduced by an arithmetic-progression step,while the metal spacing is increased by a geometric-progression step. An improved layout with variable width and changed spacing is of benefit to the Q factor of RF spiral inductor improvement（approximately 42.86%）,mainly due to the suppression of eddy-current loss by weakening the current crowding effect in the center of the spiral inductor.In order to increase the Q factor further,for the novel inductor, a patterned ground shield is used with optimized layout together.The results indicate that,in the range of 0.5 to 16 GHz,the Q factor of the novel inductor is at an optimum,which improves by 67%more than conventional inductors with uniform geometry dimensions（equal width and equal spacing）,is enhanced by nearly 23%more than a PGS inductor with uniform geometry dimensions,and improves by almost 20%more than an inductor with an improved layout.
As is well known, there exists a tradeoff between the breakdown voltage BVcEO and the cut-off frequency fT for a standard heterojunction bipolar transistor （HBT）. In this paper, this tradeoff is alleviated by collector doping engineering in the SiGe HBT by utilizing a novel composite of P＋ and N- doping layers inside the collector-base （CB） space-charge region （SCR）. Compared with the single N-type collector, the introduction of the thin P＋ layers provides a reverse electric field weakening the electric field near the CB metallurgical junction without changing the field direction, and the thin N layer further effectively lowers the electric field near the CB metallurgical junction. As a result, the electron temperature near the CB metallurgical junction is lowered, consequently suppressing the impact ionization, thus BVcEO is improved with a slight degradation in fT. The results show that the product of fTXBVcEo is improved from 309.51 GHz.V to 326.35 GHz.V.
The impact of the three state-of-the-art germanium（Ge） profiles（box,trapezoid and triangular） across the base of SiGe heterojunction bipolar transistors（HBTs） under the condition of the same total amount of Ge on the temperature dependence of current gainβand cut-off frequency f_T,as well as the temperature profile,are investigated.It can be found that although theβof HBT with a box Ge profile is larger than that of the others,it decreases the fastest as the temperature increases,while theβof HBT with a triangular Ge profile is smaller than that of the others,but decreases the slowest as the temperature increases.On the other hand,the f_T of HBT with a trapezoid Ge profile is larger than that of the others,but decreases the fastest as the temperature increases,and the f_T of HBT with a box Ge profile is smaller than that of the others,but decreases the slowest as temperature increases.Furthermore,the peak and surface temperature difference between the emitter fingers of the HBT with a triangular Ge profile is higher than that of the others.Based on these results,a novel segmented step box Ge profile is proposed,which has modestβand f_T,and trades off the temperature sensitivity of current gain and cut-off frequency,and the temperature profile of the device.
