Power SiGe Heterojunction Bipolar Transistor Research Articles

Design and Thermal Analysis of SiGe HBT with Non-Uniform Segmented Emitter Fingers and Non-Uniform Emitter Finger Spacing

A novel multi-finger power SiGe heterojunction bipolar transistor (HBT) with non-uniform segmented emitter fingers and non-uniform emitter finger spacing was proposed to improve the thermal stability. Thermal simulation for a five-finger power SiGe HBT with novel structure was conducted with ANSYS software. Three-dimensional temperature distribution on emitter fingers was obtained. Compared with non-uniform segmented emitter fingers structure and non-uniform emitter finger spacing structure, the maximum junction temperature of novel structure reduce significantly, the thermal resistance reduce, temperature distribution were significantly improved. Thermal stability was effective enhanced.

The Effect of Thermal Resistans on <i>I</i><sub>C</sub>-<i>V</i><sub>BE</sub> Fly-Back Characteristic of Power SiGe Heterojunction Bipolar Transistor

The effect of thermal resistans onIC-VBEfly-back characteristic of power SiGe heterojunction bipolar transistor is studied through theoretical analysis, computer simulations, and experimental measurements. It is found that a suitable thermal resistans can make the collector current achieve the second fly-back point before transistors are burned-out, and then returns to a stable situation. Such a thermal resistans is beneficial to the thermal stability. When the thermal resistans is small, the curve ofIC-VBEfly-back characteristic of HBT has no fly-back point. While the thermal resistans increases, the curve ofIC-VBEfly-back characteristic of HBT has two fly-back points.

Design and Thermal Analysis of SiGe HBT with Segmented Emitter Fingers and Non-Uniform Emitter Finger Spacing

A novel multi-finger power SiGe heterojunction bipolar transistor (HBT) with segmented emitter fingers and non-uniform emitter finger spacing was proposed to improve the thermal stability. Thermal simulation for a five-finger power SiGe HBT with novel structure was conducted with ANSYS software. Three-dimensional temperature distribution on emitter fingers was obtained. Compared with traditional emitter structure, the maximum junction temperature of novel structure reduce significantly from 429.025K to 414.252K, the thermal resistance reduce from 159K/W to 141K/W, temperature distribution were significantly improved. Thermal stability was effective enhanced.

Novel microwave power sige heterojunction bipolar transistor with high thermal stability over a wide temperature range

Thermal instability of power SiGe heterojunction bipolar transistor (HBT) at high current over a wide temperature range restricts the applications of the device in RF and microwave circuits. In order to improve the thermal instability, the influences of Ge profile in a base region on the electrical and thermal characteristics of microwave power SiGe HBT are studied with the aid of the model of multi-finger power SiGe HBT established by SILVACO TCAD. It is shown that for the HBT with graded step Ge profile, a higher cut-off frequency fT can be achieved due to the accelerating electric field caused by the graded step Ge concentration in the base region when compared with the device with uniform Ge profile. The influences of temperature on current gain β and fT are weakened, which avoids the drift of electrical characteristics over a wide temperature range. Although the temperature of device is lowered, the temperature of each emitter finger is still non-uniform. Considering the difference in heat dissipation among emitter fingers, a new device with non-uniform emitter finger spacing in layout and a graded step Ge profile in base region is designed. For the new device, the uniformity of temperature among emitter fingers is achieved, higher fT is kept, β and fT are less sensitive to temperature variation. Hence the thermal instability is obviously improved compared with the device with uniform emitter finger spacing and uniform Ge profile in base region, indicating the superiority of the new device at high current over a wide temperature range.

Thermal stability improvement of a multiple finger power SiGe heterojunction bipolar transistor under different power dissipations using non-uniform finger spacing

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.

Effect of bandgap engineering on thermal characteristic of radiofrequency power SiGe heterojunction bipolar transistor

As is well known, direct-current (DC) characteristic, frequency characteristic and noise characteristic of SiGe heterojunction bipolar transistor(HBT) can be improved by "bandgap engineering"(by Ge composition). However, the effect of "bandgap engineering" on the thermal characteristic of HBT has not been reported. In this paper, the effect of "bandgap engineering" is analyzed by the use of 3D thermal-electric feedback model. Considering the temperature dependence of emitter junction voltage and current gain, the expression of the minimum emitter ballasting resistance (REmin), which is necessary for SiGe HBT thermal stability, is presented. Furthermore, non-uniform ballasting resistance design is given so as to further enhance the thermal stability of device. It is found that the surface temperature of the device decreases with the increase of Ge composition in SiGe base. This is because SiGe HBT internally possesses the thermal-electrical negative feedback. For the same dissipated power, the REmin decreases as Ge composition increases, which is beneficial to the improvment of the performance of radio frequancy(RF) power SiGe HBT. These results provide a good guide to further optimization of RF power SiGe HBT performance, especially thermal design.

Multi-finger power SiGe HBTs for thermal stability enhancement over a wide biasing range

Multi-finger power SiGe heterojunction bipolar transistors (HBTs) with emitter ballasting resistor and non-uniform finger spacing are fabricated, and temperature profiles of them are measured. Experimental results show that both of them could improve the temperature profile compared with an HBT which has uniform finger spacing. For the HBT with emitter ballasting resistor, the ability to lower the peak temperature is weakened as power increases. However, for the HBT with non-uniform finger spacing, the ability to improve temperature profile is kept over a wide biasing range. Therefore, the experimental results directly prove that the technique of non-uniform finger spacing is a better method for enhancing the thermal stability of power HBTs over a wide biasing range.

A Base-Emitter Self-Aligned Multi-Finger Si1−xGex/SiPower Heterojunction Bipolar Transistor

With a crystal orientation dependent on the etch rate of Si inKOH-based solution, a base-emitter self-aligned large-area multi-fingerconfiguration power SiGe heterojunction bipolar transistor (HBT) device(with an emitter area of about 880 μm2) is fabricated with2 μm double-mesa technology. The maximum dc current gain is 226.1. Thecollector–emitter junction breakdown voltage BVCEO is 10 Vand the collector-base junction breakdown voltage BVCBO is16 V with collector doping concentration of 1×1017 cm−3and thickness of 400 nm. The device exhibited a maximum oscillationfrequency fmax of 35.5 GHz and a cut-off frequency fT of24.9 GHz at a dc bias point of IC = 70 mA andthe voltage between collector and emitter is VCE = 3 V. Loadpull measurements in class-A operation of the SiGe HBT are performed at1.9 GHz with input power ranging from 0 dBm to 21 dBm. A maximum outputpower of 29.9 dBm (about 977 mW) is obtained at an input power of 18.5 dBmwith a gain of 11.47 dB. Compared to a non-self-aligned SiGe HBT withthe same heterostructure and process, fmax andfT are improved by about 83.9% and 38.3%, respectively.

Thermoreflectance imaging of current dynamics in high power SiGe heterojunction bipolar transistors

By generating high resolution two dimensional temperature images of electronic devices and linking heat dissipation to electrical current, the authors demonstrate that thermoreflectance measurements employing a charge-coupled device can provide a useful and nondestructive method for profiling current density in electronic devices. Here they apply this method to high power SiGe heterojunction bipolar transistors (HBTs) integrated in a commercial SiGe bipolar complementary metal-oxide-semiconductor platform, measuring the current carried by each subcell and quantifying current collapse under high-bias operation. They show that current hogging for a HBT with two emitter subcells can lead to one subcell carrying 81% of the total current.

On the scaling of emitter stripes of SiGe power HBTs

The lateral scaling issues of the emitter stripe width of large-area power SiGe heterojunction bipolar transistors (HBTs) are analytically studied and experimentally verified. It is found that, due to increased parasitics along with the increase of device area, the maximum oscillation frequency (fmax) of a power SiGe HBT cannot be improved monotonically with the shrinking of the emitter stripe width, which is different from the downscaling of the low-power (few emitter stripes) counterparts. It is concluded that the emitter stripe width of large-area devices ought to be properly upscaled, relative to that of low-power devices, in order to optimize the RF performance of large-area SiGe power HBTs.

N- Si /i-p-i SiGe/n-Si structure for SiGe microwave power heterojunction bipolar transistor grown by ultra-high-vacuum chemical molecular epitaxy

The n-Si/i-p-i SiGe/n-Si structure, grown by ultra-high-vacuum chemical molecular epitaxy, was analyzed by cross-sectional transmission electron microscopy and secondary ion mass spectroscopy. It is shown that no defects are observed in the n-Si/i-p-i SiGe/n-Si structure, the interfaces between the SiGe layer and the n-Si layers are clear and planar, both the Ge and boron atoms are uniformly distributed in the p-SiGe, and the profiles of boron and Ge are abrupt from the n-Si to the SiGe layer. A high-performance microwave power SiGe heterojunction bipolar transistor was fabricated using the n-Si/i-p-i SiGe/n-Si structure. Therefore, ultra-high-vacuum chemical molecular epitaxy is one of the most promising methods for the growth of the Si/SiGe strained epilayers.

Emitter-ballasting-resistor-free SiGe microwave power heterojunction bipolar transistor

The emitter ballasting resistor is used to equalize the current distribution between the emitter stripes in power transistor, but it will degrade the output power, power gain, and power added efficiency. Experimental results indicate that the current gain of uniform-base SiGe heterojunction bipolar transistors (HBTs) decreases with the increase of the temperature above 160 K, so the current distribution is equalized by itself to some extent. Therefore, the microwave power SiGe HBTs without emitter ballasting resistor were fabricated for the first time, and the continuous output power of 5 W and power added efficiency of 63% were obtained under Class C operation at a frequency of 900 MHz. Hence, the emitter current density of the SiGe HBT's with emitter width of 6 /spl mu/m is 0.79 A/cm.

High-quality n-Si/i-p+-i SiGe/n-Si structure grown by ultra high vacuum chemical molecular epitaxy

The n-Si/i-p+-i SiGe/n-Si structure was grown by ultra high vacuum chemical molecular epitaxy, and analysed by high resolution X-ray diffraction, cross-sectional transmission electron microscopy, and secondary ion mass spectroscopy. A high-quality SiGe base layer with an abrupt interface to the Si was obtained. No defects were observed in the n-Si/i-p+-i SiGe/n-Si structure. Both the Ge and boron atoms are uniformly distributed in the p+-SiGe layer, and the changes of profile of both boron and Ge atoms are abrupt from the n-Si to the SiGe layer. A high-performance microwave power SiGe heterojunction bipolar transistor (HBT) was made from the n-Si/i-p+-i SiGe/n-Si structure. Therefore, device-quality n-Si/i-p+-i SiGe/n-Si structures can be grown by ultra high vacuum chemical molecular epitaxy.