BARITT diode

The BARITT diode ( English : barrier injection transit-time ) is a high frequency - semiconductor - component of the microelectronics , which as a diode is one of the electronic components. A related component is the DOVETT diode . The BARITT diode uses the injection and transit time properties of minority charge carriers to generate negative resistance at microwave frequencies. The minority charge carriers are injected via the boundary layer which is prestressed in the forward direction. There is no avalanche breakout . As a result, both the phase shift and the output power are significantly lower than with an IMPATT diode .

BARITT diodes based on silicon technology were manufactured until the mid-1980s. At 60 GHz, a BARITT oscillator achieved an output power of 1 mW. The component was not interesting because of the transmission power, but because of the very favorable noise behavior and its excellent properties as a self-oscillating mixer for applications in Doppler radars .

In its simplest form, the BARITT diode consists of a p ⁺ np ⁺ - (or complementary n ⁺ pn ⁺ -) semiconductor sequence. The p ⁺ (n ⁺ ) layers represent highly doped semiconductor regions. However, in the case of higher frequency applications, it becomes apparent that a structure in which a pn junction is replaced by a metal-semiconductor junction ( Schottky contact ) of the conventional p ⁺ np ⁺ - Structure is clearly superior. In the following, the functioning of the BARITT diode is therefore explained using the example of this Mnp ⁺ structure (M stands for the metal of a Schottky contact).

history

At the beginning of the 1970s, the BARITT diode emerged as a relatively easy-to-manufacture high-frequency oscillator at frequencies around 10 GHz. The functional principle of this diode (generation of a negative high-frequency resistance through the use of runtime effects) was described by Shockley as early as 1954. In 1968 Rüegg published theoretical basics and estimates about high-frequency power and efficiency of pnp-BARITT diodes. Coleman and Sze were the first to produce a functional BARITT diode in 1971 (50 mW high-frequency power at 4.9 GHz).

DC behavior

Figure 1 shows the course of the electric field E within the homogeneously doped n-zone of an Mnp ⁺ diode for different bias voltages U _o . For U _o = 0, two space charge zones are formed as a result of the p ⁺ n or the Mn transition (field profile D). Figure 2a shows the potential curve corresponding to the ribbon model as a function of the location. By applying a direct voltage as shown in Figure 1, the space charge zone at the reverse polarity p ⁺ n junction (field curve 1) expands and reaches the space charge zone at the Mn junction for U _o = U _DR (field curve 2, U _DR - transmission voltage ) .

The hole barrier e (Φ _p + U _m ) indicated in Figure 2b is reduced when the DC voltage increases further, so that some holes can overcome this barrier due to their thermal energy. A hole current is therefore injected into the active n-zone from the Mn junction. Under the influence of the electric field, the holes drift to the p ⁺ n junction and are extracted there. The field curve shown in dashed lines in Figure 1 and the associated potential curve shown in Figure 2c (the barrier is completely removed, the DC voltage reaches the value of the flat band voltage U _FB ) cannot be achieved in practice, as the diode would be destroyed by such a thermal load . Figure 3 shows the current-voltage characteristic of a Mnp ⁺ -BARITT diode. When the pass-through voltage is reached, a current begins to flow. In contrast to the symmetrical p ⁺ np ⁺ structure, there are two transmission voltages U _DR1 and U _{DR2 of} different sizes .

The curve shown in dashed lines in Figure 3 indicates the characteristic of a BARITT diode that generates high-frequency power (high-frequency rectification).

High frequency behavior

The high frequency behavior of the BARITT diode can be described qualitatively with the help of the curves shown in Figure 4. The diode bias voltage U _o is superimposed with an alternating voltage that is sinusoidally dependent on time. If the sum of the direct voltage U _o and the superimposed alternating voltage exceeds the transmission voltage U _DR (Figure 4a), charge carriers are injected into the active zone. The steep rise and fall of the current pulses I _C (Figure 4b) is a consequence of the exponential relationship between current and voltage. The injected holes drift through the active zone as a charge carrier cloud. Due to the influence of the charge carriers moving in the field, the current I ₁ is generated in the outer circle of the diode , which remains constant during the runtime of the holes. By means of a suitable choice of the diode width w (the transit time of the charge carriers is proportional to w), the running angle Θ shown in Figure 4 can be set to about 3π / 2 and thus a phase shift greater than π / between the fundamental wave of the modulating voltage and the fundamental wave of the external current 2 can be achieved. In contrast to the IMPATT diode , in which, due to the avalanche breakdown, there is already a phase shift of π / 2 between the modulating voltage and the avalanche current, the phase shift in the BARITT diode is based solely on runtime effects. The negative high-frequency resistance resulting from a phase shift greater than π / 2 can be used for undamping a resonator, ie a high-frequency oscillation can be generated.

literature

• SM Sze: Physics o Semiconductor Devices . second edition. John Wiley & Sons. 613-625 (1981), ISBN 0-471-05661-8
• U. Güttich: BARITT diodes for millimeter waves . Diss. Technical University of Munich (1986)
• U. Güttich: 60 GHz BARITT diodes as self-oscillating mixers . Electronics Lett. 22 629-630 (1986), ISSN  0013-5194
• MS Tyagi: Introduction to Semiconductor Materials and Devices . John Wiley & Sons. 323-333 (1991), ISBN 0-471-60560-3

Individual evidence

1. ^ W. Shockley: Negative resistance from transit-time in semiconductor diodes . In: Bell Systems Technical Journal . tape 23 , 1954, pp. 799-826 .
2. ^ HW Rüegg: A proposed punch-through microwave negative-resistance diode . In: IEEE Transactions on Electron Devices . tape 15 , 1968, p. 577-585 .
3. ↑ DJ Coleman, SM Sze: A low noise metal-semiconductor-metal (MSM) microwave oscillator . In: Bell Systems Technical Journal . tape 50 , 1971, p. 1695-1699 .