The piezojunction effect in bipolar transistors at moderate stress levels: a theoretical and experimental study

Abstract The piezojunction effect changes the current–voltage characteristics of a bipolar transistor when mechanical stress is applied. A good insight into this effect will facilitate its application in mechanical sensors, and also help to minimise errors in bandgap references due to parasitic stress. For the stress range and orientation in those applications, the piezojunction effect is modelled by taking into account piezoresistivity, band edge shifts, and stress-induced changes in the valence band densities of states. Experimentally, it is evaluated by stressing npn and pnp transistors from −155 to +155 MPa and measuring the collector current changes. The change in the equivalent base-emitter voltage ranges from −1.5 to 3.0 mV and shows a quite strong second-order nonlinearity. Up to high injection, it is independent of the bias. The measured curves are lower than those from the model, but share all qualitative features.

[1]  J. Wortman,et al.  Effect of Mechanical Stress on p‐n Junction Device Characteristics , 1964 .

[2]  J. D. Wiley.  Valence-band deformation potentials for the III V compounds , 1970 .

[3]  John Bardeen,et al.  The Effects of Pressure and Temperature on the Resistance of p-n Junctions in Germanium , 1951 .

[4]  Charles S. Smith.  Macroscopic Symmetry and Properties of Crystals , 1958 .

[5]  Yozo Kanda.  Effect of Stress on Germanium and Silicon p-n Junctions , 1967 .

[6]  P. Lawaetz,et al.  Valence-Band Parameters in Cubic Semiconductors , 1971 .

[7]  Conyers Herring,et al.  Transport properties of a many-valley semiconductor , 1955 .

[8]  S. Laux,et al.  Band structure, deformation potentials, and carrier mobility in strained Si, Ge, and SiGe alloys , 1996 .

[9]  C. R. Tellier,et al.  Linear and Non-Linear Piezoresistance Coefficients in Cubic Semiconductors. I. Theoretical Formulations , 1996 .

[10]  Patrick J. French,et al.  Reduction of uncertainty in the measurement of the piezoresistive coefficients of silicon with a three-element rosette , 1998, Smart Structures.

[11]  Per Ohlckers,et al.  Measurement of package-induced stress and thermal zero shift in transfer molded silicon piezoresistive pressure sensors , 1998 .

[12]  Yozo Kanda,et al.  Nonlinear piezoresistance effects in silicon , 1993 .

[13]  Robert W. Keyes,et al.  The Effects of Elastic Deformation on the Electrical Conductivity of Semiconductors , 1960 .

[14]  W. Sansen,et al.  A new uniaxial accelerometer in silicon based on the piezojunction effect , 1988 .

[15]  R. Humphreys.  Valence band averages in silicon: Anisotropy and non-parabolicity , 1981 .

[16]  M. Green.  Intrinsic concentration, effective densities of states, and effective mass in silicon , 1990 .

[17]  J. Dijkstra,et al.  Hole transport in strained Si , 1997 .

[18]  Charles S. Smith.  Piezoresistance Effect in Germanium and Silicon , 1954 .

[19]  J. J. Wortman,et al.  Characterization of p-n junctions under the influence of a time varying mechanical strain , 1973 .