Origin of 1/f noise in lateral PNP bipolar transistors
Introduction
There has been a renewed interest in lateral bipolar junction transistors (LBJTs) since the advancements in BiCMOS technologies. High gain LBJTs as well as lateral insulated gate bipolar transistors (LIGBT) have been developed [1], [2], [3]. As with other analog devices, the operation bandwidth and signal purity of LBJTs are restricted by their low-frequency noise. Since LBJTs are inherently surface conduction devices, the effects of surface states on current and noise are similar to that of MOSFETs. Some important results on 1/f noise exhibited by thin-film-silicon-on-insulator (TFSOI) BJTs have been reported before [4]. Yet, very little exists in the recent literature on measurements, analysis and modeling of low-frequency noise in advanced lateral PNP BJTs. In order to investigate the physical origin of these fluctuations, we performed variable temperature measurements on PNP LBJTs. In addition, a novel method of noise measurements was introduced where the cross-correlation noise power spectral density is measured between the base and the collector currents yielding more accurate information about the different fluctuation sources.
Section snippets
DC characteristics of the device under test
Since the base is lightly doped, the LBJT can be biased into the high-level injection at relatively low bias voltages. The high-level injection condition can be defined as the condition where the injected minority carrier density is comparable to or larger than the background doping density ND. This happens when the base–emitter forward bias |VBE| approaches the value [5],Here, kB is the Boltzmann constant, T is the absolute temperature, ND is the base doping, and ni is the
Experimental results
In our experiments, the emitter diameter of the lateral BJT is 7 μm. The emitter edge to collector distance is 30 μm. The cross-section of lateral BJT is presented in Fig. 2. The equivalent hybrid-π model for the variable temperature noise measurement is shown in Fig. 3 [7]. The noise signals measured from resistances RS=500 KΩ and RL=5 KΩ, respectively, were first amplified by EG&G PAR113 preamplifiers. Then, the power spectral density SVB and SVC were measured using a HP 3562A dual-channel
Theory and discussion
It is known that SIB originates from fluctuations in three different base current components. Fig. 2 shows the different current components in lateral PNP BJTs. The first one is the volume current IB1, which is the major component of the base current. In the event that this current component is the primary contributor to noise, according to Kleinpenning’s mobility fluctuation model, SIB should be linearly propotional to the base current, SIB∝IB, which is defined as [12]:
Conclusion
The temperature dependence of 1/f noise is studied on lateral PNP BJTs to investigate the underlying physical mechanisms. The equivalent base current noise power spectral density SIB is extracted using a novel cross-correlation technique between the base and the collector biasing circuitry. Two models are proposed for the origin of noise. For the high temperature region (310<T<450 K), surface recombination velocity fluctuations at the neutral base seem to be responsible for SIB. For
Acknowledgements
This work is partially supported by Texas Higher Education Coordinating Board Advanced Technology Program under grant #003656-0001-2001, and Legerity Corporation.
References (16)
An investigation of lateral transistors––D.C. characteristics
Solid-State Electron.
(1971)Proposed discrimination between 1/f noise source in transistors
Solid-State Electron.
(1982)Formulation of surface 1/f noise processes in bipolar junction transistors and in p–n diodes in Hooge-type form
Solid-State Electron.
(1989)Interface states at the SiO2–Si interface
Surf. Sci.
(1983)- et al.
High gain lateral p–n–p bipolar action in a p-MOSFET structure
IEEE Electron Dev. Lett.
(1992) An improved analytical model for collector currents in lateral bipolar transistors
IEEE Trans. Electron Dev.
(1994)- et al.
Gate controlled lateral PNP BJT: characteristics modeling and circuit applications
IEEE Trans. Electron Dev.
(1997) - et al.
Low-frequency noise dependence of TFSOI BiCMOS for low power RF mixed-mode applications
IEDM
(1996)